MRP is the game’s currency that you can use to purchase new planes, SP weapons, and parts. You can earn this by completing campaign missions, free missions, and completing Multiplayer matches. At the end of these missions or matches, you’ll be evaluated based on your completion time, number of kills, points, etc. The higher your score, the more MRP you’ll gain. You’ll get bonus MRP for completing a campaign mission for the first time.
After clearing a mission in Campaign, you can replay that mission as a Free Mission and the earned MRP from completing it will be added to your total. This can be very useful while during the Campaign missions since this allows you to get better planes, SP weapons, and parts. Multiplayer matches are usually very short and you’ll still earn MRP for simply completing a match (even when you’re not able to shoot down or hit an enemy), making it ideal for quick MRP farming. The only downside is that this will require a Playstation Plus subscription.