Is it possible to put iFrame embed code on thank you page?

how can if  put think on  thank you page after form is submitted -- also is there a way to put  field -- amount to pay 

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Unfortunately, it's not possible to embed a form or place an iFrame on your thank you page. What you can do is embed the form on your webpage and then redirect the form there when it is submitted.

Guide: Redirecting-Users-to-a-Different-Page

Let us know if you are referring to something else.