PHP & Paypal Flow

I am fairly new to using PayPal and PHP.

I am trying to work out the flow of my registration form and was hoping for some insight. I am selling tickets for an event. After the registration form, I have a review page were the user selects if they want to pay by check or through PayPal. If they select check, away they go and their information is submitted.

What I am struggling with is if they select PayPal and leave my site to pay with a Credit Card. At what point would you submit their information. It doesn’t make sense to me to submit it when they go to PayPal because how do i know if they actually paid.

Thanks for the help.

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