When Parallels Plesk Panel is installed, a random password is generated for the user admin, which replaces the old scheme when the same default password was used on all installations. This change was done to protect servers with freshly installed Panel from hacking by bots that use the default password.
After the installation is finished, you can set the admin's password being authenticated in the Panel with credentials of the server system power user, that is "root" on Linux systems, and "Administrator" on Windows systems. Such authentication with administrator's system account works in both cases of logging in to the Panel GUI and using API RPC.
The admin's password can be set up during the Panel initialization (this is the best way), or afterwards.
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