I didn't do anything with this for a long time.
At some stage I changed to BLE. It works differently and in my opinion it's easier to use once you understand it.
I bought two of these for testing.
https://www.nordicsemi.com/Software-and-tools/Development-Kits/nRF52840-Dongle
That was a good, and not ...

Sorry for the long delay.
Below is "my" code. I used initially the ESP-IDF sample code example_spp_acceptor_demo.c and modified it.
This is not clean code, I didn't have time to clean it up yet. But it works.
I pair my phone with the ESP_SPP_ACCEPTOR (ESP32 running with this code).
And then I use on ...

I connected an Arduino with an ESP32 with the UARTs.
I looked at the ESP-IDF API and examples and I see how bytes can be send and received.
I am sure I could use this also to send and receive text - with some extra work.
But maybe there is an easier way to do this and this is what I am asking here ...

I read only part of your post and maybe what I will write has nothing to do with what you want. But maybe …

I used an OBD adapter on my KTM motorcycle. The data was sent per Bluetooth from the OBD adapter to my mobile phone. On the phone I used Torque App to see the data.

And then I wanted to see ...

Ok, I will do that. But currently I am a little sick so maybe next week.

I was looking for sample code to create a simple application for serial communication between the ESP32 and a mobile phone.
It took a long time before I figured out how things work.

Here is some information - for a start without code.

I looked at the

ESP-IDF BT-SPP-ACCEPTOR demo
https://github ...