iCloud calendar not sending invites to Outlook calendar

Hi there,

My iCloud calendar isn't sending invites to my work Outlook calendar. The email address is correct, the calendar entry is created in iCloud and it even asks me if I want to send the invite - to which I say 'yes', but nothing is sent. It doesn't work on my MacBook, iPhone (11pro) or iPad. Can anyone help please? I'm getting double booked all over the place! Thanks :)