Device was not found on our servers. This may be because you removed it

Help please :-). my phone was upgrade to Nougat and then I had to have a factory reset done on it. Since then I’ve had nothing by issues with AVAST on it, mainly the AMS an AT. To get these two working I’ve had to uninstall and reinstall these apps a number of times and also had to delete my device from My Avast!. Initially the mobile backup was working ok and backing up, so I know it works with Nougat, but with having to delete my device etc to get AMS and AT working, the mobile backup app it now says “device was not found on our servers. this may be because you removed it. Please re-add your device to an avast! account”. My device is listed in My avast! account and AMS and AT seem to be working, although I can’t see my IMEI number but the commands, locations are working. So is this is what is meant my “re-add your device”? if it is then it’s there. I’ve also uninstalled and reinstalled the backup app after AMS and AT were working and I still got the same. So how do I re-add / re-link my device to my account. I think this is a great app and really would like to get it working again. txs