Syncing local files from Linux desktop to Nextcloud provider Cloudamo

Since March 2020 I have happily been using Nextcloud through provider site however I have not been able to sync local files for 5 days, getting the error message “405 Method Not Allowed” to “PUT” . 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
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