Here is the full list of all 21 Fallen: A2P Protocol achievements.
Level up all skills in Strength Branch
Kill everyone using only snipers in one mission
Recruit more than 3 caravaneers
Recharge your caravan's A2P
Kill everyone using only rocks and grenades in one mission
Kill everyone using only flametrhower in one mission
Perform a healing more than 5 times in a single mission
Kill everyone using only pistols in one mission
Kill everyone using only rifles and smgs in one mission
Kill everyone using only shotguns in one mission
End a mission without taking any hit
Complete a mission without losing any caravaneer
Kill everyone using only rocket launchers in one mission
Kill everyone using only melee weapons in one mission
Kill 4 enemies with one hit
Kill 10 enemies using overwatch skill
Scavenge all the available items within a mission
Level up all skills in Perception Branch
Level up all skills in Vitality Branch
Level up all skills in Agility Branch
Fully Equip all your caravaneers in one mission