Zoho email IOS client stopped receiving emails - "page not found"

Zoho email IOS client stopped receiving emails - "page not found"

Hi
My Iphone has just stopped receiving emails in the Zoho mail app - it gives me an error "page not found". I have made no changes to any settings and still receive push notifications when new emails arrive but can't load them into the app.
I've tried restarting the phone but this has made no difference.
I can still access emails via my laptop using IMAP and also the via the Zoho website
The last email I did receive was at 10:48 this morning GMT
any ideas what is wrong?
thanks
Jon