I noticed some error when activating Jetpack:
The Jetpack server encountered the following client error: Verification secrets not found
The reason was found in restricted access over IP through .htaccess to the file wp-login.php, as it turned out that access to this file can not be blocked if Jetpack is used.
That’s why I found lines restricting access and commented them out by putting the # (before each line) symbol (the lines can be in the .htaccess file located in the root directory with WordPress and in the web server configuration files), for example:
# <files wp-login.php> # order allow,deny # allow from 127.0.0.1 192.168.2.50 # </files>
If the lines were in .htaccess, then Jetpack can already be activated, if in the configuration file of the web server, then you still need to restart it to apply the changes.
Also, an error can occur because of conflicting plugins, you can try to turn them off in turn.