I have an ancient slightly mysterious full size keyboard that I bought from eBay a while ago.
I want to use it as a controller for my M1 MacBook Pro running MacOS 12.6 and GarageBand.
The keyboard has no manufacturer's mark on it, other than a logo saying "2way speaker system, general MIDI, and a number "70039" on it.
I'm connecting it to my MacBook Pro via an "Otracki" MIDI to USB interface.
The Otracki has LEDs on it, which flash when I play notes on the piano keyboard, so I'm fairly confident MIDI is getting to the Otracki adaptor. (I tried reversing the In/Out cables which resulted in no flashing lights when I played, so I think they're the right way around).
Then I plug the Otracki into a Dell USB-A to USB-C adaptor.
(I've also tried an Aukey USB-A to USB-C hub to check whether the adaptor is faulty - both work fine with other peripherals)
When I open the "Audio MIDI Setup" app in MacOS, I see a "USB MIDI interface" that is active whenever the Otracki is connected using either hub.
What I cannot get is any notes to play in GarageBand, or any other music app.
I've used other external keyboards with a direct USB-Midi connection into the MacBook and GarageBand before, so it's something to do with the keyboard/otracki config I think.
The Otracki amazon page says it doesn't need drivers. The device is detected by MacOS.
In GarageBand settings no MIDI controller is detected. Resetting MIDI drivers has no effect.