AC unit acting up (help!)

I'm sorry, I might have started this thread in the wrong spot since I'm having such a hard time finding the right category here.

I have a Samsung AC unit that I occasionally use to heat up my room.
Everything was working perfectly until yesterday, but today when I turn it on, it just sits there without blowing any warm air at all.

What kind of issue do you think I might be dealing with?

Thanks

It won't even respond to that 😢
I went ahead and pulled out the filters to clear out all the dust, but even after cleaning everything, it still refuses to heat up.

The cooling function works perfectly fine, though.
Is there any chance we've just run out of gas?

Swap out the batteries in the remote and then try selecting the heat setting again.
The filters aren't the issue here.
If it's still cooling, you definitely have gas.

It hasn't switched the valve over to the correct operating mode yet; just re-select heating and give it a moment to kick in...

Nothing to show for it again.
I suppose I have no choice but to call an HVAC technician.
It’s strange because everything was working perfectly fine until the day before yesterday—it had been set to heat for about a month now—but when I turned it on yesterday, there was absolutely nothing; the outdoor unit's fan is spinning away, yet there isn't a hint of warmth coming from inside.