You need to add your phone number as a trusted phone number for your client's Apple ID to be able to receive the Two-Factor Authentication (2FA) code on your phone so you can submit the iOS app on behalf of your client. This article describes the process of adding a reseller's phone number as a trusted phone number.
As a reseller/partner, you need an alternative option to avoid having the client on the phone to get verification codes every time you submit/publish an iOS app.
This situation can be avoided by adding the reseller's phone number as a trusted phone number in the client's account.
Note: For more details on how trusted phone number verification works, please see Apple's Manage Your Account article.
- Apple ID Account
To add a trusted phone number, please follow the steps below. Note that just for the first time you will need to be on the phone with your client.
Ask your client to log in to their Apple ID account page and have them:
a. Go to Security > Edit > Add a Trusted Phone Number.
b. Enter your phone number, select a verification method, then click Send.
2. Give them the code you will have received and have them enter the six-digit verification code to verify it.
Your phone number will have been added to your client's Apple ID account as a trusted number and from now on you will be able to receive 2FA codes on your phone.