4. Upload documents

Each payout must be backed by a supporting document. Upload an INVOICE or a CONTRACT against the customer and keep the returned file_id.

POST /v1/payments/customers/{customer_id}/upload

curl -X POST https://api-staging.checker.finance/v1/payments/customers/cus_01ARZ3NDEKTSV4RRFFQ69G5FAV/upload \
  -H "X-Api-Key: $API_KEY" \
  -H "X-Timestamp: $TIMESTAMP" \
  -H "X-Nonce: $(uuidgen)" \
  -H "X-Signature: $SIGNATURE" \
  -H "Idempotency-Key: $(uuidgen)" \
  -F "[email protected]" \
  -F "file_type=INVOICE"

Response — 201 Created:

{
  "file_id": "file_01ARZ3NDEKTSV4RRFFQ69G5FAV",
  "file_type": "INVOICE",
  "file_name": "invoice.pdf",
  "created_at": "2026-09-23T15:08:00Z"
}

Notes:

Accepted formats are PDF, JPG, JPEG, and PNG, up to 10 MB each.
Each document may back only one payout. Reusing a file_id returns 400 FILE_ALREADY_USED.
Payment documents are not listed among the customer's KYB files.