Showing st paid in st3 return

In the Quaterly ST3 return, if the Service Tax for the Invoices of May and June is paid in July, should that payment be shown in May and June columns only against the related invoice months or do we have to show it in the next return in the month where the actual payment is made?

Also when an interest is paid, should that be shown in 4B? and what will the source document number? Will that be the respective challan number.

Kindly assist. Thanks in advance.