Coupons in Event Manager

I’m starting to use coupon codes for some events we have on our event schedule. When i create several coupons with different offers…. I don’t get the option to select which to use for a specific event. They all end up showing up in the drop down menu in the coupon field when i do a test registration. I only want people with the coupon code to be able to enter it in to get the discount or free offer. Can anyone share what i might be doing wrong. Thanks!