Why can't I enter a shop code?!?

Okay I don't know if this is a glitch or not but when I find a shop code I (try to) enter it at the shop by pressing the A button once and then 3 more times quickly, after I do that the persons face seems surprised and all that stuff. Well after the face seems surprised nothing happens it just stays at the surprised face and if I wait awhile it goes back to the tamagotchi dancing around and stuff. Is this a glitch is there anything else I need to do???? Help me!! :furawatchi:

Once the shopkeeper look surprised you enter the code, if you enter it right it will show you the item you get from the code, are you entering after he looks surprised?