@Hockey_Magnet said,
"The Echo does not receive bluetooth at all as far as I can tell so it will never work with your transmitter. It only transmits to another bluetooth device. The concept is that if you have good quality bluetooth speakers you can transmit anything the echo is playing instead of listening to it on the relatively poor echo speaker."
What a snarky and completely incorrect reply. Have you been hit in the head by too many hockey pucks? Of course Echos, Dots have received BT since the beginning, and over a year ago they were given the ability to transmit BT as well. How do you think all of us who send music from our phones and other devices to Echo and Dots do this? It's via BT, that's how.
I have a small BT transmitter I can attach to an iPod to send its music to an Echo, and tonight I connected the iPod via BT for first time to play music to a Google Home. They paired and played together right away
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To rhe OP Marcot
Are you sure you have audio coming from device you plugged transmitter to, and the volume level is high enough from device and the Echo volume s up high enough?