Insufficient Remaining Store Credit but it shows I have $20.76 and can't buy a pack of $20.00

So today I want to buy a $19.99 pack inside an app but it says "Insufficient Remaining Store Credit". I just bought with my balance that I redeemed with an $25 gift card a $0.99 pack and a $2.99 pack. Today I tried to get the $19.99 pack and it says I don't have credit, but then Apple Store says I have $20.76. Someone help me plz.