Hi all - please help I'm stuck!

How do I fix the following validation error: i need to add R1.00 earning to the history payslip. I have gone to the last period of the employee's history payslip Aug 2025 - i cant get it open to add the R1.00

 Validation Error: The value of Income Source Code is incorrect. At least one income code with a value greater than zero must be specified, except if Code 4588 is completed,

Guidance would be appreciated.

Celina