iPhone 15 Gmail account login issue

The following article appears to have accurate instructions. View the following article and scroll down to the section "How to Add a Second Gmail Account Using the Apple Mail App":

The important part is that you must choose "Continue" when asked to use Google.com to Sign In. That allows the iPhone to open the accounts.google.com website to authenticate you (including any two-factor authentication).

There is no difference between adding one, or more Google accounts. The steps are always the same. What is critical is that you know for sure the usernames and passwords for each account and have the necessary 2FA as well.

[Edited by Moderator]

Please ignore that last post, the link it contained was removed due to some moderation rule. Here is a modified post:

Follow the instructions to: Add an email account to your iPhone, iPad, or iPod touch - Apple Support

Once you choose Google as account type, you must then choose "Continue" when asked to use Google.com to Sign In. That allows the iPhone to open the accounts.google.com website to authenticate you (including any two-factor authentication).

There is no difference between adding one, or more Google accounts. The steps are always the same. What is critical is that you know for sure the usernames and passwords for each account and have the necessary 2FA as well.