MATEKSYS mLRS 900MHz series using SX126x/STM32WLE5 LoRa chip are NOT compatible with ELRS 900MHz / Frsky R9 series using the SX127x. They will not bind with each other.
LoRa chip SX126x(e.g. mR900-30, E22) and STM32WLE5xx(e.g. mR900-22, WIO-E5, E77) are compatible with each other.

Download STM32CubeProgrammer from ST website
mLRS firmware:
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Connect the mR900-22 to USB-TTL module (e.g.CP210x, FTDI)
- mR900-22 RX2 - USB-TTL module TX
- mR900-22 TX2 - USB-TTL module RX
- mR900-22 V - USB-TTL module 5V
- mR900-22 G - USB-TTL module GND
Connect USB-TTL module to computer while holding the receiver boot button in.
- Select UART
- Select the COM port of USB-TTL module
- Connect
- select "Erasing & Programming"
- Tick all sectors and click "erase selected sectors"
- Browse firmware (hex or bin file) related to the hardware.
- Click "Start Programming"
- After programming, unplug USB and plug USB back in. If red LED blinks at 2Hz, the receiver is waiting for connecting with transmitter.
