Originally Posted by macrophage

Start small. Buy a coffee, a few meals, groceries NOT AT TARGET and train your card for regular spend.

BTW, how much do you need to spend in X months?
That will help us come up with a spend strategy for you.

The spending ability tool is using AMEX's internal system (similar fraud detection algorithm) to not "pre-approve" you, but to let you know if a transaction of X amount can be allowed. Notice they don't ask you what and where you will be making the purchase for. That does not matter; it will spit out approve/not approved based on dollar value alone.

Other factors such as location and time of day will also trigger card denials at times.