Add donation option to payment form

I already have a payment form that is integrated with Stripe set up. Can I add a donation option to the form so that if a user in addition to paying for a product also wants to make a donation he can do that? Or, do I have to create a separate form for that?

You already have the donation option in the form. We suggest the same way, adding donation as the label then pricing it with one (1) then enable quantity box. Note that this method still serves as a product item. It is not an actual donation, like how the Donation option in the payment configuration will appear.

If you want the item to appear as a donation to your Stripe account, you should create a new form and redirect users there if they wish to. You can put a link to the donation form in the payment form. 

Let us know if need further assistance.