Workflow stuck on payable validation

We are using EBS 12.1.3

The iexpense workflow for a particular user is stuck on server validation.

The workflow status monitor shows Project/Task validation error. Contact your support representative

Correct the errors and click Problem Fixed to validate this expense report again. If the errors can be resolved by the preparer, please provide specific instructions how to fix the problem in the Notes section and click Return to Preparer to reset the Expense Report to a Saved status.

In this case, what should I proceed for the investigation?

The error is for credit card business expense, expense type is meal (cannot be used with per diem) and the amount is 4.65