Q:

Storefront registering an account: Domain is null

I am using the Storefront with SXA (XC 9.0.3) and get a Domain is null error when registering a new account (URI is api/cxa/Account/Registration):
{"Errors":["Registration: The Domain is null and is probably not defined in Domain Manager."],
"Info":[],
"Warnings":[],
"HasErrors":true,
"HasInfo":false,
"HasWarnings":false,
"Success":false,
"Url":null,
"ContentEncoding":null,
"ContentType":null,
"Data":null,
"JsonRequestBehavior":1,
"MaxJsonLength":null,
"RecursionLimit":null}

Where should I configure the domain value?

A:

Sounds like you haven't setup your security for your Tenant/Site, or if you have, the domain is not configured. If you setup your SXA Security and pick a new domain for the tenant or site, it is not automatically added to the Domains.config file.
To configure the domain, just click the Domain Manager from the Launch Pad:

Then click New and add the domain:

This will update the /App_Config/Security/Domains.config file, so you may need to deploy that out to your CD servers too.

