XWA Upgrade

I want to include a reinforcement flight group the player can call in with Shift-S if they run into trouble. Searching the forum indicated the way to do this would be to set the Arrival condition of the reinforcements to: "100% of Flight Group [player's flightgroup] must be reinforced". However, when I run my mission and press Shift-S I get a message stating there are no reinforcements available.

Since the player is part of a two member flight group, I figured it could trip up the 100% part. I get the same result with "At least one" and "All player craft".

Stock missions use the 100% method, so that at least should work fine. Are the arrival methods setup properly?

There are 2 methods to set a reinforcement flight group.

Open the "Arrival" section for that flight group. There are 4 parameters to set in that section: arrival condition, delay time, difficulty level and the "via".
"Via" is at the bottom right.

Method 1
Arrival condition: 100% of Team [player's team] must be reinforced.
Via: You can select Hyperspace or whatever craft already in the region. If you choose a craft, please choose one with a hangar to avoid bugs.

Method 2
Arrival condition: 100% of Flight Group [player's flight group] must be reinforced (this is the option you have chosen).
Via: You MUST select [player's flight group], otherwise there will never be reinforcements available. You have probably left it to "Hyperspace".