Ibbq 4t cannot connect

I have tried everything, my ibbq 4t doesn’t connect to my wifi, I tried a combination of slow and fast flashing on the 2.1ghz network. No go, it cannot connect

any suggestions?

May I know which app you are using, is it the INKBIRD app? Or the Inkbird pro app?
Please check if the router is set up correctly. Please understand that the router settings will also affect the connection of the device.