Vehicles are not being shown as available for dispatch.

Do the vehicles have enough staffing at the station to be dispatched?

Ask if if this is a recent problem. Also, is he running any script like LSS manager?

Have him clear his temporary internet files and see if it works. If not, try a different browser and report back

Has he recently used staging areas? Myself and others in my alliance have been experiencing issues for several weeks now. A handful of units for some reason like to stick around at the staging area, even though it is no longer there.

The fix is to either find a mission that is close to the staging area, not the station it should be at. Alternatively, you will need to swap that unit with another at a different station - allowing your missing unit to then 'reappear'. Hope this helps...

Is he using ARR’s to dispatch the calls so he doesn’t have to send each individual unit? Does he have a lot of units?

I am having the same problem with one of my units. Plenty of staff, response area 400, code 2. I play on different platforms and it is not available on any of them.

Ended up trying the station swap and found out it was stuck in a bygone staging are.

This is an issue I am also having. I think that its when you have lots of units, they can't all fit on the window. The solution is to click the button I have shown below, as it loads the rest of the vehicles in. This is frustrating if you have to do it for every mission though. Hope this helps.