You have 128 Kbytes of Pebble RAM attached to an ARM Cortex M3 or M4.
This means that your entire request must match 128 KB, along with the HTTP implementation, the encryption implementation, the corresponding encryption key, and things like what you want to keep in memory (contact list, message history, etc.).
Honestly, this will not work, and the C programming language is not your problem here, so the HTTP-based encrypted protocol is not what you want to run from 128 KB of RAM.
Since your Pebble does not have an Internet connection on its own, you will need an application running on a smartphone (or any other Bluetooth device) that will talk to your Pebble - let it be your Telegram client and just show alerts on your SmartWatch.
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