Hi Sanju,
when you complete with your required inputs in f-53, then you click to process open items, the next step is you will select the desired line items you want to clear, further more you will simulate you can find the list of line items you are going to clear.
here you can double click on vendor line item whose posting key is 25, then you can see payment reference field which is in disable in my case.
the concern is how can i enable the field to input some value
i think your clear what my concern is;
Thanks,
Amjad