This error occurs because of mismatch in Client ID, Client Secret and Domain field in the account Configure page. Please click on the Authorize button in the configuration page
check the domain in your configuration.
it may be .eu or something like this
Sticky Posts
How to Add Users to your Organization in ZohoMail?
A better clarity so you can create other users to start using Zoho Mail. You can directly Add Users from the Control Panel to your Organization. You can invite users with the existing email address. If the person (user) already uses ZohoCRM, then you can import users from Zoho CRM. You can also import them using a .csv file. (if you are planning to add them in Bulk) In this topic, We will be discussing on how to Add and Invite users only. The Import options are self explanatory. ____________________________________________________________________________________________________________