Falcom | PSV Bi Zhi Track EVO Sinicization program source code

I'm writing a progressive web app for an android tablet which should be able to read and write to a device with an embedded Telit BLE module via a BLE connection.

I am able to open a BLE connection and discover services and characteristics. I am unable to establish a connection over BLE using Telit's Terminal I/O (TIO) protocol.

My remote (server) device is a Falcom Fox3 tracker unit. A notification event can be read from the Fox3 serial port when a connection is established. This has been successfully tested by connecting to the Fox3 using Telit's android terminal app: https://play.google.com/store/apps/details?id=com.telit.tiosample

I have put together a short function which should connect via BLE, establish a TIO connection and request UART credits before listening for incoming data from the server.

I have based my code on a simple script from Smashing Magazine : https://www.smashingmagazine.com/2019/02/introduction-to-webbluetooth/

The process of initiating the TIO connection follows is that given in Telit's Terminal I/O Profile Client Implementation Guide .

the Terminal I/O connection setup consists of the following steps:

• The Terminal I/O client scans for Bluetooth Low Energy devices advertising the Terminal I/O service.
• The Terminal I/O client establishes a Bluetooth Low Energy GATT connection to a detected Terminal I/O server.
• The Terminal I/O client performs a service discovery on the Terminal I/O server.
• For the retrieved Terminal I/O service, the Terminal I/O client performs a characteristics discovery.
• The Terminal I/O client subscribes to indications of the UART credits TX characteristic (see 7.4).
• The Terminal I/O client subscribes to notifications of the UART data TX characteristic (see 7.2).
• The Terminal I/O client transmits initial UART credits to the server (see 7.5).
• Once the Terminal I/O client has received the response for the transmitted UART credits, the Terminal I/O connection is considered established and indications for the UART credits TX characteristic and notifications for the UART data characteristic shall be expected at any time.

The order of the connection setup sequence is mandatory.

My code is as follows, where log is a function which outputs to the screen.