Most of the time, your customers' Member ID and Member Code will be the same. They will only differ if you have changed your Member Code.
A Member ID is created for your customer automatically when you register them. It is the number that is printed out when you print a temporary membership card via the POS. The Member ID does not change.
A Member Code is the number that you see on the backend. When a customer is first created, the Member ID will be the same as the Member Code, but you can change this member code to another number if, for example, you want to create membership cards with different codes.
When creating a QR Code membership card for your customer, it is important to use the right prefix for the right number (ID or Code):
A Member ID must be preceded with a semi-colon (;), e.g. 1001 must be ;1001
A Member Code must be preceded with an 'at' symbol (@), e.g. 1001 must be @1001