The Missions and Contracts by Rewarding are how you earn various rewards for playing the game. You can find all the missions and contracts available in the upper left part of your screen where you can see what you need to do to complete the objectives. These objectives and their rewards vary each time, from using your character's abilities to purchasing a specific item from the in-game store during a match.
The problem with Valorant players is when they complete a mission or an agent contract; none of the rewards for completing the mission are available. The same goes for those who revolve around the battle pass, which is experiencing similar issues. Each time a player completes one of the quests, they earn a reward and move on to the next, but they cannot equip or use it properly.
Developer Riot Games originally reported a fix for this series of issues. On his main Twitter account, he detailed how the issue was resolved and players could receive whatever they earned. Despite this assurance and sharing this information, players continued to report issues.
Due to all that is happening on the Riot side, there is little that players can do to correct this issue. Riot will need to manually check what's preventing players from receiving their rewards, then figure out how to make sure everyone gets their due by completing missions.
Once you find the solution to the problem, you can expect to see fewer issues each time you get rewards for completing a series of games in Valorant. The rewards will go to your account and you will be able to use them properly as you traditionally would.