Unless TTN has changed detection for single channel gateways, then: if the single channel gateway supports downlinks, then it also supports OTAA.
But indeed, single channel gateways are not compliant and using them needs a lot of tweaking, especially in the nodes to force them to use only that single channel (and SF).
As TTN is not even showing the Join Accept in the gateway’s Traffic page, maybe:
- It does not recognize the AppEUI/DevEUI or cannot validate the MIC from the Join Request. Am I right to assume nothing shows in the application’s Data page in TTN Console? That might indicate the AppKey, AppEUI and/or DevEUI are wrong. (See Hex, lsb or msb?)
- It refuses the DevNonce, see OTAA shows "Activation DevNonce not valid: already used".
- It refuses the single channel gateway to transmit the Join Accept, as it somehow detected it does not support downlinks. Does your gateway even support downlinks?
Clicking on a Join Request might give you some more information in the Trace details.
Is one of them even what you’re expecting? (Every TTN provided AppEUI starts with 0x70B3D57ED, so it seems the third might be the expected one?) Are you sure all are transmitted by your device?
You’ll need to show us the code, and tell us which LMIC you’re using, and tell us what earlier suggestions from this topic you’ve tried. (It seems GitHub - mcci-catena/arduino-lmic: LoraWAN-MAC-in-C library, adapted to run under the Arduino environment might be the most up to date?)