The nRF91M1 PPP Host Application is tested against the newest ncs-serial-modem release that ships the nRF91M1 zip for the nRF9151 or nRF9151 SMA DK. Download serial_modem_<tag>_nrf9151dk_nrf91m1.zip from the upstream release page, or use the copy at the top level of your SMHA release bundle.
This build enables PPP and CMUX on UART0 routed to the host (P0.27/P0.26 TX/RX, P0.15/P0.14 RTS/CTS, DTR/RI on P0.31/P0.30). Without the nRF91M1 variant, the modem listens on the USB VCOM UART instead, and the host sees init_chat_script: timed out.
Extract the zip and flash the .hex on the nRF9151 or nRF9151 SMA DK:
nrfutil device program --firmware serial_modem_<tag>_nrf9151dk_nrf91m1.hex --recover
CI on-target tests resolve and flash the same archive before each 91m1 run. See Serial logs.
To match an unreleased Serial Modem commit instead, build the modem application yourself; see the Serial Modem getting started guide for workspace setup and build arguments.