Form does not submit after PayPal transaction unless user clicks

I have payment of a membership fee required in my form through PayPal, where clicking "submit" at the bottom of my form takes the user to the PayPal interface. Payment processes fine, but the user's form submission is not processed or delivered to my integrated Google Sheet or email system unless the user clicks "return to merchant" after their PayPal transaction goes through. How can I ensure that the user's form submission is processed the second their payment goes through?

Unfortunately, this is not possible since this is being controlled by PayPal. It is required to click on the link in order to return to the form to complete the transaction. The post transactions will be processed once the form is redirected from the PayPal window. 

Hope this information helps!