Error 403 while attempting to watch a video

[joedmru]

Environment: Windows 10, PMS 1.14.1.5488.
I successfully installed and authorized YouTubeTV plugin at google.com/device.
I'm able to list categories & videos, also can search them.
But I cannot play videos neigher with my LG TV nor by Plex Desktop Web client.
After a while after I press 'Play' button it reports about an error in transcode.
I looked into PMS log files and found this entry
ERROR - [Transcoder] https://r2---sn-xguxaxjvh-a23e.googlevideo.com/videoplayback?c=WEB&hightc=yes&mime=video%2Fmp4&initcwndbps=1231250&ratebypass=yes&ipbits=0&fvip=4&requiressl=yes&nh=%xxx&itag=22&expire=1550972410&lmt=xxx&sparams=ctier%2Cdur%2Cei%2Chightc%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Clmt%2Cmime%2Cmm%2Cmn%2Cms%2Cmv%2Cnh%2Cpfa%2Cpl%2Cratebypass%2Crequiressl%2Csource%2Cexpire&ctier=A&mn=xxx&mm=31%2C29&key=yt6&ip=xxx&dur=5816.227&pl=22&source=youtube&ms=au%2Crdu&ei=xxx&id=o-xxx-xxx&pfa=5&mv=m&mt=xxx&signature=: Server returned 403 Forbidden (access denied)
I deleted some values from the url in order not to expose tokens which could be related to me - replaced by xxx, but 'signature' key has no value initially.