Proving my "worth."

The mysterious thief brought up a similar story upon our encounter a few months ago.
It was about winning a game against them.
Last time, I lost and missed the thief by a hair's breadth.
I tried to corner them with more people than I have now,
but they seemed to have seen through everything already.

Things are different now. I’ve realized that for them, numbers don’t matter.
Which is also precisely why I came all the way here alone.
I’m not sure why they're so obsessed with this proof thing...
But if that’s what it takes to get the pendant back, I’ll have to play along one more time.

I moved closer to where the mysterious thief’s voice echoed in the darkness.
But as expected, they have vanished once again,
leaving only a firmly locked door in their place.
It looks like an entry code is required. Is this also a form of proof?
Written below was a mysterious string.


@68+101+116+67+105+101+108