Clarifying previous question about Google Chrome Extension.
I need to access the textboxes inside an iFrame.
I believe I am accessing the iFrame because I can get at the height, width, and other attributes of the iFrame itself, just not the content within. I don't think this is a same origin policy issue because from what I can tell the iFrame uses the same domain.

For reference this is the Spotify Checkout page where it asks you for your credit card, etc to start a free trial.

Screenshot of iFrameHTML: https://ibb.co/YhNSHth

var iframe = document.querySelector('iframe.iframe-pci');
iframe.querySelector('input#cardnumber.form-control').value = "1234123412341234";   

and

var iframe = document.querySelector('iframe.iframe-pci');
iframe.querySelector('input#cardnumber.form-control').value = "1234123412341234";