You might want to be a bit more specific with your situation to get help on this. For example, telling us where the error message comes from (PC or TV).
“HDMI from PC to TV” sounds like a HDMI cable running from your PC to your TV, so your problem would either be the display looking weird or not working at all. This scenario doesn’t usually give error messages.
“HDMI dongle to my TV” sounds like you’re either using a HDMI Receiver dongle (like Steam Link) or you’re using a smart TV dongle (like Amazon Fire TV Stick). If it’s a Receiver, you may need to re-pair your dongle to your Tranceiver that’s sending it the signal. If it’s a Smart dongle, you probably need to set it back up using whatever smartphone app it tells you about on screen.
“Device decryptor request failed” in google shows posts for USB failing to handshake and tell the PC what the device connected actually is. That shouldn’t apply to HDMI unless you’re using a USB to HDMI adapter.
...and that’s all I got from your description.