Setup has detected that the Website "{0}" is already using the port that you have selected to install Dynamics 365 Server. ...

Setup has detected that the Website "{0}" is already using the port that you have selected to install Dynamics 365 Server. You must specify a unique port to create the new site. If you want Setup to install Dynamics 365 Server to use this port, you must reconfigure the existing Website "{0}" or specify it for the Dynamics 365 Server installation.