Validation errors

When you make a payment using POST /payment-request, the API validates the request body before processing. If the request contains errors such as missing required fields or invalid data formats, the API will return a 4xx status code along with detailed error information in the response body.

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The API checks all required fields in nested objects such as Recipient.Account.AccountNumber. If any part is missing or invalid, the request will fail with detailed validation messages.

You must fix the errors and resubmit the request.

Typical validation error structure

{
  "errors": [
    {
      "field": "ExampleField1",
      "message": "Example error message1"
    },
    {
      "field": "ExampleField2",
      "message": "Example error message2"
    }
  ]
}

Common validation errors and how to fix them

Error Message	Cause	How to Fix
"The field `field` is required."	A required field is missing.	Add the missing field to the request.
"The field `field` must be a valid ISO 4217 currency code."	An invalid currency code was used.	Use a standard 3-letter currency code, for example `GBP`, `USD`, `EUR`.
"The field `Email` is not a valid e-mail address."	The email format is incorrect.	Check for typos or formatting issues.
"The field `Name` must be a string with a maximum length of 250."	The input exceeds the character limit.	Shorten the string to meet the maximum length.
"The field `AccountNumber` can only contain numeric characters."	Letters or symbols were used in a number field.	Remove non-numeric characters.
"The value provided for `ExternalReference2` is not allowed."	A denylisted value was used.	Choose a different value or contact support.
"`SendAccountId` is not permitted for this user."	The account ID doesn’t belong to the user.	Use an ID returned by `GET /accounts`.
"Either `StoredRecipientId` or `ExternalStoredRecipientId` must be provided."	No recipient ID was included.	Include one of the two identifiers.
"`SendValue` must be greater than 0."	A negative amount was entered.	Use a positive number for the amount.

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Use the Rules section in MAS under Money Out > Rules to determine country-specific field requirements.

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Some fields (like ABA code for USD to US) are required only for specific currencies and recipient countries.