In a terminal type:
host -t ns <domain>
Make sure these match the nameservers YOU have set in squarespace.
Check in incognito mode in chrome because it caches results.
https://account.squarespace.com/project-picker?client_id=helpcenter&redirect_url=%2Fsettings%2Fdeveloper-tools make sure there are no API keys here, if there are, remove them
https://account.squarespace.com/project-picker?client_id=helpcenter&redirect_url=%2Fsettings%2Fcontributors Make sure the accounts YOU control are owners
https://account.squarespace.com/settings/security/two-factor
https://account.squarespace.com/project-picker?client_id=helpcenter&redirect_url=%2Fsettings%2Fcontributors Remove any accounts you dont recognise