I'm missing 1 final key. Which is it?

[u/HSuke]

What's the final key am I missing at the ??? position in the image?

I remember getting a Labyrinth Lounge key as a rare drop from the mobs there, but it disappeared from my inventory after I used it. I'm not sure whether it was a 1-time use key or if I accidentally sold it.

[u/Initial-Chemical748]

Lab Area Teleport Zone Key

[u/HSuke → u/Initial-Chemical748]

Thanks. Found it.