Facebook Ad Account is attached to no other page...yet can't connect through Shopify??!

[celiza]

While I am admin in some capacity on different Facebook pages, my ad account is attached to none.

However, when I try to connect my account, I get this message:

This ad account needs to be added to the selected Business Manager to continue. <Button: Add Account>

When I click <Add Account>, it then gives me this message:

This ad account couldn’t be added to the selected Business Manager because you’ve reached the maximum number of allowed ad accounts. Contact Facebook support to learn more

Why is this happening and what can I do to fix it?