How to have payments and donation on same paypal?

You should be able to do so by creating products with regular field and https://www.jotform.com/help/275-How-to-Pass-a-Calculation-to-a-Payment-Field

For example:

1) You can create products with radio button field:

2) For each product, you can assign calculation value which will be the actual price for the product:

3) I added "Donation" as product so a field could be revealed when it is selected:

And it will be revealed with this condition:

So users can enter a custom amount.

4) Then I do the calculation in the Form calculation field:

That calculation is passed to payment so users can be actually charged:

You can check how it works here: 

https://www.jotform.com/91056591195967

Hope it helps.

Thank you!