iPhone Calendar not syncing with Microsoft 365 Business Exchange Email

I have my own domain name and use Microsoft 365 Business Exchange. It has been working but I noticed today it isn't.

All other aspects of the account such as contacts and mail are working and I have deleted and reset the account.

I have gone over the calendar settings to ensure that it is working.

The exchange calendar works fine on my MacBook.

I notice that in Calendar settings for my account it says 'unable to update calendars'.

Very odd, never happened before. I assume it is temporary and a bug or issue in an Apple Server somewhere.