If your own Apple account does not have the Two-factor Authentification activated, your customers who have it activated can allow you to publish with their account, from your own account.
Your customer must invite you in their Apple Development Team:
Go to developer.apple.com
- in “People” section click on “Invite people“.
- Then they have to enter your Apple account email in “Invite as Admins” field and click on “Invite“.
A mail will be sent to this address and you will have to accept the invitation.
Go to AppStore Connect
- in “Users and Roles” section, click on + next to Users
- They have to fill the First Name and Last Name and add your Apple account email then click on Next.
- Then they have to check “App Manager” as Role and click on “Next“.
- Keep the settings on “No Territories” and click on “Save“.
Finally, from your Siberian, while using the iOS Auto-publish, click on “Refresh available Teams & Providers”:
The new team will be displayed in the list. Select it and start your publication.
Note: only “Company/Organization” accounts can invite people to join their Apple Development team.