When receiving the below error, please first make sure you have more than one user license on the license you are using to activate on the server. If you have confirmed you have more than one user license and the error persists, please continue below.
The other reason for the error is likely caused by the iFilter plugin being pushed out with the software. The iFilter plugin built into the .msi package is meant for Desktop use so it is triggering the error.
You will need to create a .mst file through the Customization Wizard with the setting to disable the iFilter plugin.
Please see here on how to use the Customization Wizard Tool to create a .mst and deploy it: https://kb.foxitsoftware.com/hc/en-us/articles/360040241172-Generate-transform-MST-files-via-Customization-Wizard
Please see here to find the Customization Wizard Tool version compatible with your version of the Foxit Software: https://kb.foxitsoftware.com/hc/en-us/articles/360040659931-Available-Foxit-Customization-Wizard-Tools-for-Foxit-PDF-Editor-for-Windows-version
The specific setting you are looking for within the Customization Wizard tool is under Features. You will want to select iFilter and set it to "Entire Feature Will Be Unavailable"