In order to be able to build and submit your iOS app an invitation to your Apple Developer Account is required.
Note that this will only work if you have an Organization Account.
Below you can find more details on how to invite users to it.
Access the Apple Developer website clicking here. On the top right section, you can click on “Account” to be redirected to the login form.
You can then insert your login credentials to sign-in into your Apple Developer Account
Once logged in you will see your Apple Developer Account Dashboard. There you can click on “People” in the left sidebar.
On the “People” area of your Apple Developer Account you can then click on “Invite People”, the button will be located in the middle of your screen.
Insert the email that you would like to invite into the form that will be displayed and proceed with clicking on “Invite” to send the invitation.
That’s it! An invitation email will be sent to the selected email.