Hello everyone.

I am trying to add a feature in my website where users can make a payment. The amount to be payed is calculated via PHP on my site, and I need to pass this value along some other variables located in my PHP, to the Paypal payment page. However, I have not been able to achieve this and it makes me wonder if Paypal even offers this possibility in the first place.

I made a diagram that shows more or less what I am trying to achieve:

Basically, I tried to insert a Paypal 'Pay Now' button on my site, but when the user clicks it, it prompts for payment amount input, which makes it useless for me. I need that Paypal checkout page to display the amount to charge with the variable I'm passing to it. I know that I can add variables to the button on creating via the Paypal website, but it only allows me to set static prices.

Apart from this, I also would like to know if when the transaction finishes succesfully on the Paypal payment page, do I get some sort of return value/signal that lets me know if there was a success/error ? I need this signal in order to do some other processes on my website with PHP.

I would greatly appreciate help, I'm at a total loss and I need to implement this badly for a serious project I'm working on.