Hi @gavin1,
By default, you should be able to use the same email address in different connections. If you’re using WordPress, your issue might be similar to this post: All of a sudden: "There was a problem with your log in: There is a user with the same email." - #5 by ADeweyan.
For automatically linking accounts, I recommend these docs:
You’ll also find more information about implementation in its subchapters.
If you have any other questions, feel free to reach out.
Have a good one,
Vlad