How to receive custom amount payments in Paypal which are NOT donations

I have made a form to pay with paypal, the amount is read by a variable from a calculation, but this only takes it as a "donation" see: https://www.paypal.com/mx/cgi-bin/webscr?cmd=_flow&SESSION=uzWB5NKgfCdgligA6o6tlPYmRkhmMfeprYCvhd2ihzyzwpEYClKDHbhMgXi&dispatch=5885d80a13c0db1f8e263663d3faee8d64ad11bbf4d2a5a1a0d303a50933f9b2 is there any way to change this to a normal buy layout? This is a donation window and my form is not for donations is for selling a product/service. (I didn't find the option of reading a variable in products selling in your paypal option panel).

Use the product options instead.

This guide will also help you to achieve it.

Your second question has been moved to this thread: http://www.jotform.com/answers/767576.

We will assist you there.

But Sell products doesn't read my calculation field, only custom amounts that I set. People choose different options in my dropdown menus and depending on what they choosed the price changes in the calculation field. Then paypal reads this calculation field with Custom Amount Payments. But can I achieve this with Sell products?

The only way to have a custom amount passed from your calculation is to use the "Collect Donations/Custom Amount Payments" option. It is not necessarily for donation, but also for any custom amounts:

http://www.jotform.com/help/275-How-to-pass-a-calculation-to-a-payment-field

Make sure that the option "This is a donation" is not selected if you are not receiving a donation:

Please let us know how it goes.