Sorry for the problem of being unable to install Joomla. I just checked this issue on a test server and it installed without any problems (Joomla version 3.9.11). The easiest way to install Joomla is to log in to your cPanel and then use Softaculous (application installer). It will install Joomla for you. Remember that it must have an active domain name to be properly installed. InMotion accounts are typically associated with a domain name. The installation application (Softaculous) will use that domain by default during the installation. If you already have a website (other web-based apps) at that location, then there is a possible conflict. Make sure that the location you're using for the installation is free of any possible conflicting installations. If you continue to have problems with the installation, you can contact our live technical support team to investigate the matter further.
I hope this helps to answer your question. If you need further assistance please let us know!Kindest regards,Arnel C.