Why Can't I Buy Guns at the Armory Station??

[Shadowfox]

I have plenty of money. It says "gun reserved"

??

[Voragon]

same here,

[Veassen]

It's a common bug, as where you buy guns in Exhibition with the help of a trainer, prior to receiving your loadout from Pavel.
Can only be fixed by starting a new game.

There are reports of people claiming they didn't use a trainer, but they are quite rare.
Whatever the case, there is no other solution as to continuing with the guns you have, or replaying.

Can always try to reload the chapter.
Maybe that will fix it, but don't get your hopes up with that.