I've created a new Payment part, but when I try to select it to use on my Donation Form part, it is not listed. Why is it not presented as an option?
On the Donation Form part, you are selecting a Payment page rather than a Payment part. To utilize the Payment part, insert the part on a page. Note: If you are using a Payment 2.0 part, the Payment 2.0 Summary part must also be inserted on the page.