Warning: Any work with high voltage equipment can be dangerous or even fatal. It should be performed by a qualified electrician. Please ensure that you comply with local electrical codes and regulations. Improper installation can lead to device failure and even cause a fire. Damage to thermostat due to improper installation is not covered under warranty.
Before you install Mysa, you should use the online compatibility checker, here. This will determine if your heating system will work with Mysa. If you are certain that your gang box has only two wires, then Mysa is not compatible with your wiring and cannot be installed. Also, just because one gang box only has two wires, it does not mean that other gang boxes in your home also do. Please ensure to check other boxes.
My existing thermostat only has two wires
The amount of wires connected to the existing thermostat is not an indicator of your compatibility for Mysa. Please be sure to look in the gang box, your existing thermostat wiring does not necessarily indicate how many wires are in your gang box.
As you can see in the picture below, there are only two wires connected to the existing thermostat, but there is a third one in the gang box. This scenario is compatible with Mysa.