Which microbit extension are you using?
Probably it is much better to send commands via UART, interpret these on your microbit and set the io-pins using makecode on your microbit.
See here: The Internet of Things: Data Acquisition and Analysis for a tutorial.
Of course you are using a bluetooth extension, but my question was, which one.
Actually it does not matter because you cannot address the io-pins this way, because all microbit extensions are flawed. You can only successfully use UART, read my previous post again. try the tutorials I pointed to, and then try your IOpins again.
At this moment you cannot address the IO-pins of the microbit directly from App Inventor, as I said. So, what you should do instead is send a command to the microbit via the serial interface UART, the microbit recieves this command and activates the IO-pins, using MakeCode. All explained very well in the IOT tutorials.
The last example in these tutorials is about watering plants, I think also do via the IO pins, so that should help you.