Bluetooth cannot send data successfully

Hi everyone , I am new to app inventor and I would like to ask some questions about BluetoothLE .

The problem is that I cannot send data successfully with bluetooth.
Since my code is too large, I just post the part of sending data with bluetooth, but I will describe other part rapidly. Below is my sending data code.

My goal is to send a string from my phone to Bluetooth module HM10. I've used another ready app to check whether HM10 module received data normally. And the answer is yes, the motor works correctly. So my MCU code should not be incorrect.
Thus I think the problem should be in the program I posted.

I will be very grateful if anyone can help me solve the problem.
And if needed, I can provide other part of my code or information.
Thank you very much.

I belive you need another block "RegisterForStrings" nefore the call to WriteStrings,
that will complete the connection process

Try setting utf16 to false.

Also show what exactly the command_str variable contains. Display this data in a label and take a screenshot. You can send a maximum of 20 bytes of text at a time.

Thanks for some suggestions.
I add a label(Label 66) to show what the command_str variable contains.
It contains nothing. But why?

the command_str variable is a string to join each component in string_list with a " "(space).
Here's the code of string_list.

The string_list variable contains empty text fields.

But I change the contain of text box, which means changing the string_list. So I expect the command_str should be changed also.

I've used a label to check that string_list contains value. So, I don't know where is the problem.

By the way, I found out that using bluetooth between two screens seems to cause disconnection problems. However, my phone screen did not show the "connection error" message. How can I whether bluetooth in the second screen works normally?

The bluetooth connection does not work across screens.

You can use virtual screens.