Syncing local files from Linux desktop to Nextcloud provider Cloudamo

Since March 2020 I have happily been using Nextcloud through provider site fr.cloudamo.com however I have not been able to sync local files for 5 days, getting the error message “405 Method Not Allowed” to “PUT https://fr.cloudamo.com/apps/dashboard” . I have tried in Windows [I normally use Linux Mint]. I use 2 browsers, Firefox and Brave and it’s the same problem in both of them. I updated the calendar from my phone and that has synced ok, but not the files on my desktop PC. The primary caldav address remains unchanged as https://fr.cloudamo.com/remote.php/dav
Any advice would be appreciated. Cawchapin
Linux Mint 19.2 Tina 64-bit
Kernel Linux 4.15.0-163-generic X86_64
MATE 1.22.0
memory 3.8GB
Processor AMDFX-4100 Quad-core
Available disk space 124GB