Billing Cycles -Periodic

Hi Community, 

I came across Greg_Deckler Periodic Billing Which pretty much did the work I needed.

However - How to apply the billing cycle? as Greg_Deckler shows monthly record. 

Customer     Start Date             End Date              Amount        Cycle
A                  04/04/2021           05/04/2022       30             Monthly 
B                 15/04/2021          15/04/2023        50              Bi-Annually 
C                30/04/2021           30/04/2022       20               Quarterly 
Required  to show as below; 

1. Quarterly = if billing is April 2021 , the next is in Aug 2021  and so on 

2. Bi-annually= if billing is April 2021 , the next is Oct 2021 

Would really appreciate.

Thanks