unfortunately there seem to be some LilyGo T3_V1.6.1 433Mhz boards around which are causing issues.
I assume you have left the Erase Flash check box ticked when uploading lilygo-rtl_433 through the web upload?
If a fresh upload doesn’t seem possible - try holding and letting go of the RESET button on the LilyGo board when the upload initiates - you could also try the step suggested here to completely erase the flash and try the web upload again.
Some othersi n the team and myself have exactly the same board version and have not come across this unfortunate behaviour.
@DigiH Here is the update. I tried again option 1, but this time using a Windows machine and Edge. Success with upload from web at first try. For info failed attempt was with macOS running BigSur 11.7.4 and Chrome.
On a MacBookAirM1 that needed complete setup, after loading the drivers for the CH9102 serial port chip, the OpenMQTTGateway web installer worked perfectly fine. Hmmm, so I went back to the iMac15,1 running BigSur, downloaded the ch34xser_macos and installed. Voila! OMG Web install also worked perfectly on the configuration. So it was a group7 failure (“equipment not a fault”).