How do I log in to a client's sub-account, switch back, and find one sub-account among many?

1. Go to Settings, then Sub-accounts, and click Log in as this tenant. It opens a new window on a different domain, so you can work in both accounts at once.
2. Use the account switcher bar at the top in the middle to move between accounts. Click your own account to go back to it, or click your logo on the left to see the list of sub-accounts you can search or click into.

The switcher lists only recent accounts. If you have many sub-accounts, search for the person under Contacts. A sub-account owner has a small user icon next to their name. On their contact, the Billing tab on the right shows what they bought, their transactions, a way to reset their password, and a Log in as button to jump into their account.

After you log in to a sub-account, a banner at the top shows when that sub-account has a zero balance.

A teammate who is an admin on your main account can always log in to your sub-accounts, so they do not need to be a user on each sub-account too.