You may be looking to integrate TrepStar with PayPal if you're already using PayPal for order processing. However, some publishers already have PayPal IPN turned on with a notification URL to a web site other than ours. There is not a way to add a 2nd PayPal IPN Notification URL but there is a work around.
You can easily add a 2nd PayPal linked account for your TrepStar orders. This will not interfere with your current PayPal account and it will use your existing bank account.
Please call PayPal's new account setup group at 888 - 847 - 2747 and ask them to help you set up a 2nd account that is linked to your existing account. This linked account will deposit money to your existing bank account. All you need is a new email account for this 2nd linked account.
Once you have the new linked PayPal account, you can follow the instructions on how to add TrepStar as the IPN notification URL.
Look at this video about trepstar and paypal IPN.