Follow these steps to install an addon in Blender:
Download the addon: Download the RBC Addon file, this can be found Blender Market or Gumroad
Open Blender Preferences:
Navigate to Add-ons: Click on the Add-ons tab in the Preferences window
Install the addon:
Click the "Install" button at the top of the Preferences window
Browse to locate your downloaded addon file
Select the file and click "Install Add-on"
Enable the addon:
Find the newly installed addon using the search bar
Check the box next to the addon name to enable it Note: When updating to a new version disable then enable the addon to refresh.
Note: When Upgrading from Free version to the Pro make sure to disable the free version first.
Save Preferences: Click "Save Preferences" to ensure the addon remains enabled when you restart Blender