FuseClick system donot supply Stay Rate value directly, However you can calculate it manually using multiple event offer feature.
One offer can be have up to 10 events, But for Retention rate calculations, the offer must have atleast following two events - Install and Uninstall.
 When advertiser receives the completion of install, it will pass the conversion of install to FuseClick by Postback URL, and the conversion of this initial event will be recorded in the Conversion Reports.
Similarly, when advertiser receives the completion of uninstall, it will pass the conversion of uninstall to FuseClick by Postback URL, and the conversion of this uninstall event will be recorded in Conversion Report.
The calculation method of Retention rate: please check  two event's conversions by Event name or Event token in conversion report; Find out how many conversions of install event and how many conversions of uninstall event; For example, The conversions of install event are 100 and the conversions of uninstall event are 50, then the formula is Retention Rate = (install conversions - uninstall conversions)/ install conversions * 100% =(100-50)/100*100%=50%.