You can use this API to determine if the parameters are correct. The body is the same as /financial/v2/transaction/execute endpoint. The callerUniqueReference will be reusable after the validate call is complete. Note: You don't need to call this endpoint before an execute as all transactions will be validated before they execute. This is useful if you are using a new rail and want to check your parameters.
curl --request POST \
--url https://api.mpay.com.au/financial/v2/transaction/validate \
--header 'accept: application/json'