Shelly 2 is discontinued and replaced by Shelly 2.5

The Shelly 2 is fully supported in Tasmota from version 6.2.1.7

DO NOT CONNECT ANYTHING TO ANY GPIOs OF THESE DEVICES!!! (No sensors, no switches, nothing)
The GPIOs on the Shelly are connected to AC power! Only use a Shelly as designed.

Do not connect AC power and the serial connection at the same time The GND connection of the Shelly is connected to the live AC wire. Connecting serial with your PC will fry your PC.

Check the correct jumper position before connecting AC power to Shelly 1. If the jumper is set to 12V you will destroy your Shelly!

An ESP8266 with 2MB flash dual relay device with Energy Monitoring the size of round 45mm.

The inbuilt template equals the following:
{"NAME":"Shelly 2","GPIO":[0,135,0,136,21,22,0,0,9,0,10,137,0],"FLAG":0,"BASE":47}
An alternative template without switch pull-up is:
{"NAME":"Shelly 2n","GPIO":[0,135,0,136,21,22,0,0,82,0,83,137,0],"FLAG":0,"BASE":47}

The shelly 2 inputs may or may not need pullups for SW1 and SW2 to work correctly. Default state is pullups enabled.

To disable pullups either use command SetOption62 1 or select the option from the GUI.

Refer to the following issue: https://github.com/arendst/Tasmota/issues/4841