Please note: Custom forms should only be implemented if you have the in-house development bandwidth to do so. We are not able to troubleshoot custom forms beyond this documentation.
If you are using a direct link layout, navigate to Dashboard > Funnel > Content > Contact Form.
If you are using a segmenting layout (e.g. thumbs, faces, stars), navigate to Dashboard > Funnel > Content > Interaction Design > Unhappy Customers.
Click the Present With... dropdown menu and select Custom (the default is Contact Form).
Once you've pasted your code, click OK, then Scroll down and click Update Content to save your changes.
Note: this feature is not available when using the Review First layout.