Why does the Direct Test Mode app (v3.x.x) fail to communicate with my BL65x?

Answer

Recent changes to Nordic’s DTM commands appear to have introduced compatibility issues with the DTM implementation in the BL65x smartBASIC firmware. Please use Direct Test Mode app version 2.5.3 within nRF Connect for Desktop, which worked successfully in our testing.

All tested versions (v3.0.0, v3.1.0, v3.1.1, v3.1.2, v3.1.3, and v3.1.4) produce the same error.