How can I setup a multiple payment form?

Is there any way to make Paypal optional? I want to give my clients the choice to either pay online or pay in person, but I am not entirely sure if that's possible. 

From how you described it, you wanted to give 2 payment options for your users - Either to pay online (PayPal) or in person (Purchase Order). Since you can only have 1 payment field per form, the only way around this is to create a multiple payment form, which requires 3 forms:

1. 1st form: The main form that will conditionally show 2 more forms (for PayPal and Purchase Order).

2. 2nd form: Online payment using the PayPal payment field.

3. 3rd form: In person payment using the Purchase Order payment field.

We have a very detailed guide that will walk you through this process. The example given on the guide below uses the Purchase Order and PayPal payment fields.

Complete guide: How-to-Create-a-Basic-Multiple-Payment-form