This is, I’m afraid, @phillxnet’s expertise so I’m unsure of the root cause of the issue here. In the meantime, you should be able to workaround this by disabling quotas (they are currently not enforced).
@aremiaskfa I found that for resizing currently the quotas need to be turned on. I usually have them turned off. When I wanted to perform a resizing some time ago (on 4.1.0-0), I needed to turn quotas back on for the pool where I wanted to perform a resizing of a share.
For some reason, in my case the change in the WebUI didn’t hold, so I had to do it at the command line…
btrfs quota enable /mnt2/<volume_name>
and then after resizing or creating a new share, I disabled them.
I just tried it on my 4.6.9-1 installation … and this time it didn’t complain about it, so not sure whether I did anything different or something has changed, but I am also running on the Linux: 6.3.1 now (backport for Leap 15.4) so a new version of btrfs-progs might have taken care of that problem …
I guess, if currently have quotas on, then @Flox 's recommendation is the one to follow, and if you currently have them off, then you can see whether following mine addresses it. But as mentioned above, since we’re not enforcing quotas the resizing would be only for visual/cosmetic purposes at this moment.