curl --request POST \
  --url https://matcher.sandbox.lerian.net/v1/config/contexts/{contextId}/sources/{sourceId}/field-maps \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '{
  "mapping": {}
}'

{
  "contextId": "<string>",
  "createdAt": "<string>",
  "id": "<string>",
  "mapping": {},
  "sourceId": "<string>",
  "updatedAt": "<string>",
  "version": 123
}