AppsBuilder won't in any way directly charge your clients for the Apps you supply them with.
That's why it's important for you to set up your own payment process with them, via the channel you prefer best. Here are a few suggestions.
For easy one time payments:
For Payment Gateways Check Out:
For Recurring Payment System:
You can link the payment page you've created to your CMS by pasting the URL in the dedicated box under the Options section:
Click on Advanced from the top menu bar:
And then paste the URL of your payment page in the Link for Pay App box:
Remember that this box will only be visible to you if you set an expiration time for your App.
Also, AppsBuilder does not provide the set up of a payment page amongst its services, so you will have to set the page up yourself and then easily follow these steps to integrate it to your AppsBuilder CMS.