If you are trying to connect Zoho Bookings to your Microsoft 365 calendar, for example to sync availability with Outlook, and the sign-in fails with a Microsoft prompt asking you to "explain the reason" for the request before it stops, this is almost always caused by the admin consent settings on your Microsoft Entra ID tenant (formerly known as Azure AD), rather than anything in the standard Microsoft 365 admin centre.
In the Microsoft Entra admin centre, go to Entra ID, then Enterprise Applications, then Consent and Permissions, then Admin Consent Settings. Confirm whether user consent is currently restricted for your tenant. If it is, individual users will not be able to approve the Zoho Bookings connection themselves, and this is often what triggers the "explain the reason" prompt.
Go to Entra ID, then Enterprise Applications, then Activity, then Admin Consent Requests. If a request for the Zoho Bookings application is sitting here, it will need to be reviewed and approved before the calendar sync can proceed.
If the Zoho Bookings application already appears under Enterprise Applications, open its API Permissions page and select Grant Admin Consent for [Your Organisation]. This applies the permissions across the whole tenant, rather than just to whichever admin account approved it initially.
Some tenants are configured to require user assignment for enterprise applications. If this is set for the Zoho Bookings application, each staff member who needs their Outlook calendar synced will also need to be explicitly assigned to it, on top of the tenant-wide consent granted above.