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.
  1. Create a Payment page
  2. Add your new Payment part to the page
  3. Edit your Donation Form part
  4. Scroll down to Payment setup
  5. Mark Use payment part
  6. Select your new Payment page
  7. Click Save