1 Click Updating doesn't work

Hi,

When I try to use 1 click updater I receive

Could not download update. The server returned an unexpected content type: text/html; charset=UTF-8

Any ideas? I don’t see any other errors in logs, cURL in PHP is enabled, I don’t have any similar issues in other projects I did. This specific project was made originally in EE2 but was updated over time to the 5.3.1, but this 1 click updater feature never really worked- it always ended on the very same problem and I needed to update manually.

Best regards!