Installing Wyze thermostat c-wire adapter without a control panel

I have an old heat pump and it doesn’t have a control panel - just these 4 wires. These wires correspond to what’s connected to the current thermostat but I’m not sure where I would be putting the c-wire from the adapter?! I’ve seen similar scenarios on here but they had a 5th connection. Please help!

Do you have a schematic or a model number of this device? Also, a picture of the inside of the unit would be helpful, from far away enough that i can see the wires in their entirety.

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