The correct format for creating a QR code for Point of Sale is: mobilepaypos://pos?id=<beaconId>&source=qr 
Example: mobilepaypos://pos?id=123456789012345&source=qr 

Please be aware that it is all lowercase. The POS beacon id is either a 15 digit number (no letters) or a GUID.

the format is both for sandbox and production environment.