If the person has sent in their mailed payment, make sure you update the record to show the amount paid so no amount is still due. If nothing is due, the user will not be sent to PayPal to make a payment. Also, each field has a parameter where you can mark is changes to that field will trigger the change fee for your event (if you have one). So make sure your fields are set as desired for the change fee... and that the change fee is set as desired in the event setup.
When teams sign up, they have the option to pay or not pay for side pots until event night. We require a partial payment of the registration amount and that ensures their registration is secured. As it's currently set up, it's impossible for them to modify their registration in any way until they pay in full which is not required. Our only work around otherwise would be to remove the partial payment as it disables any participants ability to modify their records.