Fairly easy to understand, basically if you have received the email you're eligible for the promo, if you don't check emails then just check your account as it's automatically applied.
I've just checked my account and even though it says only participating locations, all the cafes that do pickup are showing a purple banner specifying $5.50 taken off, so we've got a wide selection here.
Enjoy and don't overdose on caffeine ;)
"Selected users" implies it is targeted and not available to all.
* Just pointing out that other users would tag this one as [Targeted] to clarify.