The logic isn't correct
One of the reasons that make this issue is when your form logic has more than one ending. So it causes it to work incorrectly.
Since you want your form to redirect to the payment page, your Logic should have only one ending.
The following steps can help to fix this:
Remove the "Submit form" rule in all situations and ensure only one field submits the form.
Add a content field at the end of your form to show the final payable price and encourage the user to submit & go to the payment. Then, because it's the last field, it automatically submits the form.
Finally, change the logic on the parts that were to "Submit the form". Instead, jump to the last content question.