SWYH play on Google Music


nowadays Google Assistant enabled speakers are becoming very common, probably will sell millions in USA as Christmas presents, I already have one of these and I am trying to stream.
to do that I play some music files on my windows PC and use SWYH, as there is no direct way to stream to Google speaker I get the SWYH stream on my apple iphone using a custom radio I have created on Tunein or similar internet radio apps, and this works fine , I can listen to streamed music on my iphone, from there on I try to cast the music to the google speaker, there it stops and does not play, the tunein app also stops and indicates no media to play.
can you advise me what I can do to solve my problem. actually there are other ways to play my computer music on google device, my actual aim is to play small group amateur radios broadcasting on FLATCAST or similar.
thanks and best regards