Thanks for the info and confirming. Also, just to check, do you have the Steam Overlay enabled? As this is required for any in-game purchases to work.
If the issue still persists, then next I recommend to try Verifying Integrity of Game Files:
- Right-click Vermintide 2 in your Steam library sidebar
- Select ‘Properties’
- Select the ‘Local Files’ tab
- Select the ‘Verify Integrity of Game Files’ button
- When complete, close and reopen Steam