Admin authentication keeps spaming on quota change

I want change user quota in User tab, which triggers an autentification request. On typing the password, I am prompted again with no other message. If I enter incorrect message, I am warrned about it. This repeats over and over.

Any ideas?

Is there way to set quotas manually e.g. from command line?

Nextcloud version: 12.0.2
Operating system and version: Debian 8 (latest)
Apache or nginx version: Apache (latest packed in Debian)
PHP version: 5.6.30
Is this the first time you’ve seen this error?: yes

no: How change email quota and admin-group using OCC?

Do you get any errors in your Nextcloud logfile? A quick look in the developer tools don’t hurt either.

Sorry for the late response.
It turned out, that it was caused by wrong server time.