There are 2 reason that you may be getting a fatal error when installing Ultimate Client Dash Pro:
1. Ultimate Client Dash Pro is an add-on of Ultimate Client Dash the free version. This means that you’re required to have the free version installed and activated before you can install and activate the pro version. You can read more in our online documentation here: https://ultimateclientdash.com/docs/installation/
Note: There are protocols to display an alert message and to automatically disable the pro version if a user tries to activate it without the free version activated, however, we have noticed some users reporting that their hosting company has ignored these protocols.
2. If you’re trying to install Ultimate Client Dash on a multi-site setup you will get a fatal error as the plugin is not compatible with a multi-site setup. This is something we do plan on integrating in the future.