thanks for your inquiry.
Unfortunately TWINT and PostFinance Card are not supported to work in an iFrame as it is only available OffSite, which means on the Page of app-wallee.com. You will need to configure the payment method integration so it redirects to this page when the payment is confirmed. You can see how it looks here:
You can see the available supported methods per paymentmethod here:
If you have any further questions, please reply to firstname.lastname@example.org and mention the ticket number 56539 so we can help you most efficiently.
Hope I could help you.
With friendly greetings