Walkthrough of Matze's Great Scavenger Hunt

Step 2

The last hint clearly talked about some collection of "old Euro Bank Notes" that Mathias has.
Maybe this pile of money? But those look like the new Bank Notes...
A Heap of Cash

Anyway, it looks like it's been the right thing to look for after all! Was his collection of old Bank Notes replaced by the new ones?
The Cash with a visible QR Code

That would explain why matze was told to letitgo. Using this information, we should be able to read the next hint