Everything you do in a match is calculated at the end and giving as a coin reward, with goals offering up to 200 coins, so make sure you keep scoring even against pitiful opponents. pass accuracy also pays out based on your percentage completion (% = coins), so towards the end of the game try to pass the ball around your backline to boost the number a bit. Possession is the same, so keeping the ball with your defenders for the closing stages will help prop this number, too.
Basically, the better you perform on a higher difficulty, the more cash you stand to earn.