IMAP stopped working after installing a VPN

I recently installed a VPN on both my computer and mobile, I had a few notifications from Zoho mail about unrecognised IP's logging into my mail account and then the after a couple of days IMAP stopped working on my account completely. I can still access mail from Zoho app and browser but both OSX Mail and IOS Mail both report that they are "unable to verify account name or password."

I was on an unpaid plan from back in 2017 which had always worked with no issues with IMAP. Since the issue I read that you had to pay for a hosted mail client with IMAP so I have upgraded to a payed plan but the issue has persisted.

I have updated my mail servers from imap.zoho.com smtp.zoho.com to the imappro.zoho.com smtppro.zoho.com, changed my password in Zoho, deleted both accounts and reinstated them multiple times on both devices with the VPN switched on and off, but still have had no joy, and would really like this email back in with all the rest of my accounts in Mail on Mac and iOS.

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