Hi @Brizzle76
Welcome to the Sonos Community!
I am sorry hear of this issue you are having with getting your Firestick to play via Bluetooth to your Era 300 speaker.
Do you get audio when you connect, for example, your phone to the speaker and play? If not, please try rebooting the speaker by unplugging it from power for a moment.
If you do get Bluetooth audio when using your phone but not when using the Firestick, please try rebooting the Firestick by removing it’s power for a moment instead.
If you cannot get audio playing through your speaker when any device is connected, I recommend you get in touch with our technical support team who have tools at their disposal that will allow them to give you advice specific to your Sonos system and what it reports.
I hope this helps.
Hi @Corry P
I was getting audio fine via Bluetooth connection to my phone so tried your suggestion of rebooting the firestick and it’s now working! 
Really appreciate your help with this and hopefully this will help others if they experience the same 
Hi @Brizzle76
Fantastic! Thanks for coming back and updating the thread!