Didn't work for us either. We still can't reconnect the Facebook Channel.
Finally we have reconnected. This is how we fixed the issue, with Shopify support - Just check you only have yourself as an admin, not any other functions.
Please go to your Facebook Page > Settings > Pages Roles > and review the roles here. Ensure their Page Roles are set to "Admin” rather than "Jobs Manager" or "Custom". In order to be connected successfully, the permissions will have to be set to "Admin".
If the below options are enabled in the Facebook Business Manager account, the page role will appear as “Custom”. If you disable these options, they will be recognized as a standard page "Admin" and be able connect to the Facebook Sales Channel as expected.
to get there Click Business settings>Select the page>Disable the two options
Once complete, please review that the Facebook Business Page settings look like the screenshot on the right, via Facebook Page - > Settings -> Pages Roles. Then connect to Facebook.