Error activating Pro Sites

Hi, I’m getting the following error when network activating Pro Sites. Reading through the boards, all the erros were due to older versions of php. I have 5.5.38 (also lists this in dashboard support).

Error:

Plugin could not be activated because it triggered a fatal error.

Fatal error: Cannot redeclare class APIClient in /home/…./…./wp-content/plugins/pro-sites/pro-sites-files/lib/ProSites/Module/Taxamo/lib/Taxamo/Swagger.php on line 28

Thanks