I’m trying to connect to my Google My Business account but it’s saying my posts are disabled because Google has flagged this location as a chain.

If Google has flagged your location as belonging to a chain you are currently limited from post scheduling to your Google My Business profile as determined by Google's internal detection process.

These rules are outlined in the Google My Business API here:

If you are not part of a chain, you can contact Google directly to request to update your Google My Business account details. Contact the Google help centre here.
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For further information on chains, please contact our support team.