They represent the real-time movement of funds between accounts across all Pix participants, following the technical and regulatory standards established by the Central Bank of Brazil (BACEN). Pix transactions are designed around speed, traceability, and interoperability — ensuring consistent behavior regardless of the institution or front-end channel.

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Key characteristics

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Pix transactions share a common foundation across all institutions:

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Instant settlement

Funds typically settle within 10 seconds, with SPI guaranteeing completion or timeout handled transparently.

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24/7 availability

Pix operates continuously — including weekends, holidays, and outside business hours.

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Irrevocability

Once a Pix is completed and credited, it cannot be reversed except through regulated flows (Refunds, Devoluções, MED).

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End-to-End ID (E2E)

Each Pix transaction receives a unique E2E identifier for auditability, reconciliation, and dispute handling.

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Interoperability

Any Pix participant can send or receive Pix from any other, independent of institution, platform, or channel.

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Configurable limits

Institutions must enforce regulatory and internal limits for security and fraud control.

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How a Pix transaction works (End-to-End Flow)

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Below is a simplified cross-institution view of a Pix transaction:

1. Initiation The user starts a Pix transfer using one of the available addressing methods:
   • Pix key
   • QR Code (static or dynamic)
   • Manual bank details
   • Copy-and-paste EMV code

1. Authentication & authorization The sending institution must authenticate the user with strong mechanisms (e.g., biometrics, 2FA, device trust). User consent is mandatory.
2. Validation & risk checks Before sending anything to SPI, the institution must validate:
   • Account condition (active, not blocked, KYC verified)
   • Balance availability
   • Limits (transaction, daily, nightly, monthly)
   • Pix key validity (if applicable)
   • Risk assessments (anti-fraud indicators, velocity checks)
3. Settlement attempt (SPI) The institution submits the transfer to SPI (BACEN’s Instant Payment System), which:
   • Validates the message
   • Routes it to the receiving institution
   • Settles the transaction between institutions
4. Credit to receiver The receiving institution must credit the account immediately, even if:
   • It occurs outside business hours
   • Systems are under load
   • Amount is high (except for flagged anti-fraud cases)
5. Notifications & E2E generation
   • Both institutions receive the updated transaction status
   • The transaction receives a unique E2E ID
   • Webhooks or internal notifications update systems and users

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Pix Transaction types

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Pix transactions fall into a few standardized categories governed by BACEN.

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1. Cash-Out (Send Pix)

The payer sends funds to another account using a Pix key, QR code, or bank details. Flow (summary):

1. User initiates transfer
2. Institution checks balance + limits + key
3. Transaction is sent to SPI
4. Receiver credits instantly
5. Both parties receive updates + E2E ID

Common scenarios:

• P2P transfers
• Merchant payments
• Bill splitting
• Marketplace split payments (when paired with Pix Cobrança)

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2. Cash-In (Receive Pix)

The customer receives a Pix transfer from any other institution. Flow (summary):

1. Receiving institution is notified via SPI
2. Account must be credited immediately
3. Notifications are dispatched for reconciliation
4. Transaction is recorded with E2E ID

Common scenarios:

• Salary or corporate disbursements
• Merchant settlements
• Recurring customer payments

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3. Refund (Devolução)

Regulated flow that allows institutions to return funds to the original sender. Refunds may be triggered by:

• Customer request
• Merchant refunds
• Duplicate payments
• Operational errors
• Fraud-related MED cases

Refunds must:

• Use BACEN standard messaging
• Be linked to the original transaction
• Follow value and eligibility rules

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4. Reversal (Chargeback / pacs.004)

Used in special regulated cases — often tied to MED or operational corrections. Reversals follow strict BACEN rules and are not the same as merchant refunds.

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Intra-ledger Pix transactions

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When both accounts belong to the same institution:

• The transfer does not pass through SPI
• The institution processes it internally
• E2E ID may still be assigned for traceability
• All standard validations apply (limits, fraud, balance)

This mode reduces latency and external dependencies while preserving Pix semantics.

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Validation layers (Regulatory + Operational)

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Every Pix transaction goes through multiple validations before being sent to SPI:

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1. Account checks

• Account active
• Not blocked
• KYC complete

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2. Funds availability

• Sufficient balance
• Temporary holds released

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3. Pix key validation

If the user pays via key, the recipient’s details must be fetched from DICT and confirmed.

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4. Regulatory limits

• Per transaction
• Daily limit
• Nightly limit (mandatory)

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5. Risk & fraud checks

Institutions may enforce:

• Velocity checks
• Device fingerprinting
• Behavioral analytics
• Known-fraud markers

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6. Idempotency

Each Pix transfer must have a unique transaction ID. This avoids duplicate transfers during retries.

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Operational controls and safety

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Authentication requirements

Strong customer authentication is mandatory for all Pix send operations.

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Notifications & Webhooks

After crediting, institutions must notify systems and users. Webhooks allow real-time reconciliation.

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Error handling

Common error categories include:

• Timeout
• Invalid key
• Insufficient funds
• Daily/nightly limit exceeded
• Suspicious transaction blocked

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Auditability

Pix mandates full traceability:

• Logs
• Timestamps
• E2E ID
• Account metadata

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Transaction limits (BACEN Rules)

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Pix transaction limits exist to reduce fraud risk, protect end users, and maintain operational safety across the instant payment ecosystem. BACEN defines minimum security standards, and institutions may add additional restrictions depending on their risk appetite. Pix limits are divided into mandatory regulatory limits and institution-defined limits.

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1. Mandatory regulatory limits (BACEN)

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Nighttime limit (Per-Transaction Cap)

Institutions must enforce a lower maximum limit between 20:00 and 06:00. Regulatory requirements:

• Default maximum: R$ 1.000
• Institutions may set a lower default (e.g., R$500 or R$ 200)
• Customers may reduce this limit instantly
• Customers may increase this limit only after a minimum wait of 24 hours
• Customers may adjust the nighttime window (e.g., extend to 18h–08h)

This rule applies to:

• Pix transfer (cash-out)
• Pix QR Code payment
• Pix Saque/Troco
• Pix Cobrança payments initiated at night

Its purpose is to prevent fraud during higher-risk hours.

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Allowance for Customer-Controlled limits

Institutions must offer customers the ability to configure their own limits, per:

• Transaction
• Day
• Nighttime maximum
• Other forms of risk-based segmentation

These changes must respect BACEN timing rules:

• Reductions → must take effect immediately
• Increases → can only take effect after a minimum of 24 hours (security delay)

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Obligation to analyze requests for limit increase

Every institution must:

• Accept customer requests to increase limits
• Evaluate them through risk criteria
• Grant or deny based on fraud policy
• Apply increases only after the regulatory waiting period (24h+)

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Saque/Troco limits (Cash-Out at merchants)

Pix Saque and Pix Troco have their own caps:

• Default: R$ 500 per transaction
• Institutions may voluntarily offer up to R$ 3.000 per transaction
• Customers may reduce this limit instantly
• Increases follow the same 24h rule

These limits do not affect normal transfers — they are specific to cash withdrawal modalities.

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Credit obligations (independent of limits)

Even if limits are exceeded, once a Pix is credited to the receiver:

• The transaction becomes irrevocable
• Only MED or refund flows can reverse it
• Institutions cannot “undo” a completed Pix on their own initiative

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2. Institution-defined limits (Configurable)

Beyond mandatory rules, institutions may add their own controls, such as:

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Per-Transaction limit

Maximum allowed amount for a single Pix operation.

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Daily limit

Cap on total Pix amount per user per calendar day.

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Monthly limit (optional)

Used mainly by corporate accounts or fintech risk models.

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Risk-based segmentation

Institutions may offer:

• Stricter limits for new customers (ex.: first 7 days)
• Different limits for high-risk users or flagged accounts
• Dynamic limits adjusted by customer behavior

These internal controls must never conflict with BACEN requirements — only complement them.

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3. Operational rules required by BACEN

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Immediate limit reduction

Customers can lower their limits instantly.

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Delayed limit increase

All increases must respect:

• 24 hours minimum before becoming effective
• Optional additional waiting period (institution’s choice)

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Peak risk hours

Nighttime limits apply specifically to cash-out flows, as they represent the main vector for fraud losses.

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Real-time enforcement

Institutions must check limits before sending a transaction to SPI. A Pix that violates limits must be rejected locally, not after reaching SPI.

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4. Limit behavior in transaction lifecycle

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During a Pix initiation

The sending institution must verify:

• Available balance
• Transaction limit
• Daily limit
• Nighttime limit
• Saque/Troco limit (if applicable)
• Fraud/velocity limits
• Customer-configured limits

If any rule is violated → transaction must be rejected with an appropriate code.

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During retries

Limits must be validated again. Idempotency prevents duplicate transfers but does not bypass limit checks.

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During merchant flows

Dynamic QR Codes must also respect:

• Customer limits
• Time-of-day rules
• Saque/Troco caps

Even if the merchant sets an amount, the payer’s institution decides whether to approve.

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5. Recommended customer communication

BACEN requires institutions to:

• Explain limits clearly
• Offer customer self-service to adjust limits
• Show pending increases and activation dates
• Notify customers in case of suspicious behavior

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6. Summary table