Hey Olavah,
If you check on the code where you call the iframe and pass some parameters such as the Consumer Key and Secret, you will see paramater "$callback_url" - That is the link that is loaded once payment has been completed
If you cannot access the code, kindly copy the address on the link that is on "Click here to continue" where you say the page gets stuck and confirm that it's a page that can load from your browser
