Error 507: Bluetooth can't connect to Adafruit Bluefruit LE Shield

I'm new to app inventor. I have no coding experience nor I have created an app before, but I'm trying to create an app to control 4 servo motors via Bluetooth.

I have checked multiple videos and tutorials but I'm struggling with the first: connecting my tablet (Fire OS with Adafruit Bluefruit LE Shield.

Here are my Blocks so far:

This is my Designer View:

My tablet is Paired with the Adadruit Shield, and it turned ON

When testing the App and I hit Scan, the Adafruit appears in the ListPicker

But when I select from the list, it can't connect and gives Error 507:

Can anybody help?
Thanks so much in advance

From the display on your tablet, you are paired with a BLE device but not with a basic BlueTooth device.
From your AI2 component list, I see only the basic BlueTooth Client component but not the BLE extension.

Suggested reading:

Hello ABG,
Thanks for the information. I went ahead and imported the Bluetooth LE extension ( BluetoothLE extension (version 20200828)] from the site recommended

However, this doesn't fix the problem. Actually, now with the BLE extension, no devices appear on the list after Scan, while with Bluetooth Client1 the Adafruit BLE device appears on the list. I'm attaching screenshots of the block and the result of the device Scanning with BLE extension:

and with Bluetooth Client1:

I'm a bit puzzled!. It seems from the readings recommended that BLE should work with my Adafruit device and tablet.
I have also tested this first step for the connection with my phone (Google Pixel 4) with the same results as with the tablet (no devices detected with BLE extension, Adafruit detected with Bluetooth Client1).

Thanks for your help

I apologize for the delay in responding.

I have no more expertise in BLE to offer you.
I defer to the other board users with more experience in this.