You must include a payment term in the invoice so that the customers know when they must pay the outstanding charges. You can create multiple payment terms, but only one payment term can be made default at a time.

Change in the payment term during an ongoing contract is considered a disruption because it can have a significant impact on the flow of the revenue of the contract. When a change in payment term is initiated (as a part of an ABO or individual change), the existing billing schedule records are superseded and new records are created, irrespective of any global billing setting or configuration.

See Change In Billing Rule for example.