Why can ProSite not be activated after installed?: Plugin

Why can ProSite not be activated after installed?:

Plugin could not be activated because it triggered a fatal error.
Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM in /kunden/268552_55268/chem-tools/MultiBrandPage/wp-content/plugins/pro-sites/pro-sites-files/lib/ProSites/Module/Taxamo/lib/Taxamo/Swagger.php on line 185