Custom domains is our way to confirm, that you actually own the domain you wish to implement our forms on.
Confirm a domain
To whitelist a domain, you need to navigate to Account -> Domains.
On the right side of the table you will find a text field, where you can type in your domain. The domain needs to be entered like "domain.com". There should not be added http / https, www or any other path after the domain, as it can make conflicts during the approval process.
After submission you will be required to send an e-mail under the newly created domain, where an e-mail will be sent for you to confirm.
Click the confirmation link in the e-mail, and your domain will be confirmed and approved for use.
From here you can also enable this domain as a sending domain, which you can read more about here: Sending domains