I’m not complaining, but I just checked my mail before getting off and I had 40k Vanguard vouchers. The message just said for me to claim my reward and didn’t tell me what I did. I really wanna know. Xc
You get them by winning battles in Sector Conquest.
If you win a battle in each of the two sectors under attack that your faction is engaged in, you get 20k vouchers for winning at least one battle there.
Two sectors, two sets of 20k. 
Awesome!