403. That’s an error.

Your client does not have permission to get URL /api/manifest/dash/as/fmp4_audio_clear%2Cwebm_audio_clear%2Cwebm2_audio_clear%2Cfmp4_sd_hd_clear%2Cwebm2_sd_hd_clear/hfr/all/mt/1556295513/requiressl/yes/itag/0/fvip/3/ei/lC_DXNbFCJvnkgapprGYCA/expire/1556317172/key/yt6/playback_host/r5---sn-o097znlk.googlevideo.com/mm/31%2C26/ipbits/0/mn/sn-o097znlk%2Csn-nx57ynls/pl/24/signature/87CB0B8CE92C784F8439BED4775B05FE34DDAE1D.3562DDCD91E301E93DCD5538F26397A33E4F5E14/source/youtube/mv/m/initcwndbps/173750/ms/au%2Conr/ip/206.189.73.156/sparams/as%2Cei%2Chfr%2Cid%2Cinitcwndbps%2Cip%2Cipbits%2Citag%2Cmm%2Cmn%2Cms%2Cmv%2Cpl%2Cplayback_host%2Crequiressl%2Csource%2Cexpire/id/129900620604ce5e&title=Let's+Play+Portal+2:+Episode+5 from this server. That’s all we know.