how to debug payroll run

 hi,dears, i run payroll process, then run prepayments, but there was no record in pay_pre_payments.
i tried very hard to find out that this is due to payroll process failed to produce taxable income
entry. i am new to payroll, i think there would be some way available and convinient to let us know
what happened during the payroll process, ie, find out why some results must be produced but failed.

i tried to use debug PYUGEN, set pay_action_parameters DEBUG parameter, but i can not understood the output.

can somebody tell me how do you debug when face such issues.