Here is the error: Item missing. See https://steamerrors.com/26
Hey! You should definitely read this thread Official Statement: PUBG "Personal Trades" Turned Off
The quick synopsis is that PUBG devs have banned personal trades of in-game items so the Gameflip BOT can’t trade the items back to you.
I believe Gameflip are waiting to see how this situation resolves itself as PUBG initially advised that they were going to instigate this change and ponder a way forward.
I recently read that they are happy with the current state and the ban on personal trades will become permanent.
Until something definitive happens your items are effectively trapped in the trade bots