Network invocation on a real device needs https？I am using a http interface ,but to find some works and some doesn't？

As JIM said in some thread, it's it better to use the https protocol. But due to policy I cannot get a ssl certificate right now. So is it ok to use http on real devices?Or only some devices?

I found some users are able to use the http interface,and most of them failed to use it. Is there any place to set the http request policy like use https only or allow http insecure requests on the GCM.  Besides if you encountered any issues in the http request, welcome to share~ Thanks~

https://forums.garmin.com/developer/connect-iq/f/discussion/229138/http-or-https-server-connections-best-practice/1083562#1083562

MY code is here:

https://pastebin.com/SnS3Emi0