In 2020, Must developed new WIFI Plug instead of previous WIFI RTU. It works for our PV1800 and PH1800 series MPPT solar inverter with 48V as following:
PV18-3048 VHM, PV18-4048 VHM, PV18-5048 VHM, PV18-5548 VHM
PH18-3048 PLUS, PH18-4048 PLUS, PH18-5048 PLUS, PH18-5548 PLUS
These models inverter can work with WIFI Plug and WIFI RTU.If you still have WIFI RTU.
For more detail of this new WIFI Plug Connection, here is a Guidance Video https://youtu.be/bCEOLQoSR2c