First, thank you for making this free.
Second, I do not believe everyone understands just how brilliant this package is. You keep all of the intellectual property, as it should be, and I get a quality app.
I'm working on BT to/from Arduino. Two points.
1st. You have to do the 'Permission' step to get data in ListPicker. Also, the BT device must be previously paired to show up on ListPicker, The MIT App Inventor 'Delimiter' needs to be Hex 10, ie: LF and last, the 'IsAvailable' is >= 0 and ReadData was changed to '-1' to get all data to Delimiter.
The Arduino should use 'Serial.println() to send a LF at the end of Serial.print.
This took a long time to research and I'm better for it.
Thanks again, guys.