Payables XML can't perform a substring to a concatenated string inside a for-each

Summary:

When creating a payment request, we need to have all invoice numbers concatenated in the same field "Ref" from the XML template. However, the bank only allows length = 35.

When trying to apply a substring to that concatenation and creating a new payment, it returns an error.

Content (please ensure you mask any confidential information):

In this structure, when trying to apply a substring to a concatenation inside a for-each, it is not working.

Version (include the version you are using, if applicable):

24D

Code Snippet (add any code snippets that support your topic, if applicable):