Transactions for invalid customer references

Creating a transaction with a customer reference that does not exist now returns a clear error instead of a generic 500 Internal Server Error. You can fix the reference in your request without treating the failure as an unknown server problem.

• A customer reference that does not match an existing customer returns a specific error instead of "Unhandled error encountered."
• Bulk transaction submissions use the same validation, so invalid references are reported consistently across batch requests.
• Your integration can tell a bad customer reference apart from a transient server failure and avoid pointless retries.
• Error responses point to the customer reference problem, so logs and support tickets lead to the right field faster.
• Reconciliation and automation that create many transactions at once fail predictably when a reference is wrong instead of stopping on an opaque server error.