How to automatically calculate the amount based on the answer in the payment form?

You can use the Peergateway addon to dynamically calculate the amount based on the answer and collect payments in your google form.

Setup payments

Prerequisite: You must have installed the Peergateway add-on for Google Forms. If you haven't installed the add-on yet, you can install it from G Suite marketplace using this link.

Step 1: Open your form in Google Forms. Click on the addon icon and click Peergateway.
Step 2: Peergateway menu will be displayed. Click Configure payment.
Step 3: Configure payment setup wizard will be displayed. Select Paypal and click Next.
Step 4: Enter your paypal.me link, select the payment currency and click Next.
Step 5: Select Form field and click Next.

Configure payment amount

You can setup your form to collect a fixed amount, dynamically calculate the amount based on the answer or add custom formula to calculate the amount. In this example, we will setup the form to dynamically pick the amount for the field.

Step 6: Select the field from the form and click Next.
Step 7: Click Preview.