Hi, 

Need a bit more information. 

On an invoice - payment terms can drive different installments for a given invoice. An invoice then can have multiple due dates, for example 25% due month 1, 25% due Month 2, 25% due on month 3 etc.  Installments change / assign due dates on an invoice. 

A Period Allocation is very different it allocates (for example the revenue) into N periods for example 25% month 1, 25% month 2 etc.   These allocations do not change the invoice dates. It simply allocates the revenue into N periods. 

The easiest way to test the period allocation is to test using an instant invoice where after a line is created you can open the period allocation rule.  

Hope this helps. 

Best regards, 

Thomas

Thanks for quick response!