I want to use a different form of invoice for each class in my business. How do I select another invoice format when I do my customer invoices?

We can do that by clicking the Customise button at the bottom part, ernest3.

Before doing so, make sure that we've created a customised invoice form.

Once done, we're good to select them as your invoice form style. We can do that by clicking the Customise button located at the bottom part of the invoice. 

I've added a screenshot as your reference:

If you want to record multiple payments into a single record, you can check this guide: Group Multiple Payments Into a Single Record.

I'm just a post-away if there's anything that I can help with. Keep safe!