Substack's third-party payment processor, Stripe, is required to verify that their account holders are operating with valid addresses and contact information. They may reach out to you to verify your domain.
Failure to verify your domain can result in billing for your publication being temporarily paused, so if you're asked to do so, we recommend providing the information below as soon as possible via the prompts in your Stripe dashboard:
Email Address (within Substack domain): firstname.lastname@example.org
Support Website: support.substack.com
Terms of Service: substack.com/tos
You may want to contact Stripe Support for specific questions about the domain verification process, but you can always submit a support request here to Substack if you have additional questions or concerns.