Thanks for getting back to me.
I shall wait regarding the notifications issue.
With respect to invitations not being received. I tried this out with a family member and set up their email account on my Mac as well. I sent through an ordinary email to the address and an invitation from my Cyphr app on my iPhone 6s with the latest iOS software. The standard email was received but the Cyphr invitation was not.
I tried this a number of times and no Cyphr invitations are being received and nothing is in Junk or Spam mailboxes.
Sending and receiving phones are iPhone 6s and SE on latest iOS
Invitations sent to iCloud and Outlook accounts
Further invitations sent using web page in Firefox
Any further advice would be welcome.