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Sorry to hear you’re facing problems 
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Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 18.0.2): last
Operating system and version (eg, Ubuntu 20.04): windows 10 pro
PHP version (eg, 7.1): 7.4
The issue you are facing:
After updating the application to 3.0.1 under Windows, I cannot connect to the server. Version 2.6.5 works fine.
Error reported when trying to connect
406 not acceptable to get my_server_adres / status.php
Is this the first time you’ve seen this error? (Y/N): Y