To the best of my knowledge, only organizations and not individual Apple developer accounts are eligible for adding an additional member who has access to certificates, identifiers and provisioning profiles.
Role Permissions: Access to Certificates, Identifiers & Profile is an additional privilege for users with the App Manager, or Developer role that are members of an organization’s team. If this privilege is added, the user sees certificates, identifiers, and profiles associated with all of your apps.
A few workarounds:
This requires some trust, but you can login on the 2nd developer's Xcode with your own account which would allow Xcode to automatically manage the certificates. This is a super simple, quick way of working around this for small companies. You could also share your password, but this would require more trust.
You can request to upgrade your membership to an organization. This requires you to have a D-U-N-S numbers, which depending on the process, would take from days to months.
You can have the 2nd developer to develop on their own account with their own bundle identifier then switch it to yours. This is super slow and annoying since you may have to duplicate some of the services (like Firebase) that bind to a bundle ID.
I am looking into the possibility of signing certs and preparing provisioning profiles on my computer and emailing them over, but so far, haven't found a working solution here.
Overall, this is an unfortunate decision by Apple. It shouldn't require a creation of a legal entity and go through a month long process just to add an additional iOS engineer to the team. The situation is also exacerbated by their half-baked team management system for Individual Apple Developer program, where you can add developers, but you can't actually have them develop on device 😢
