You can retrieve up to a certain number of Coins a day from Supply Drops.

If you reach the daily Coins limit, the coin icon will no longer appear on the side of Supply Drops, and you will not receive any more until the following day. 

If you activate a Supply Drop, but do not receive any resources, it means you have reached the limit for all available resources at that Supply Drop. 

As you level up, your Supply Drop daily Coin limit will increase! Here is the Coin limit for each player level:

Level 1: 3000 Coins
Level 2: 3400 Coins
Level 3: 4200 Coins
Level 4: 4800 Coins
Level 5: 5400 Coins
Level 6: 6000 Coins
Level 7: 6600 Coins
Level 8: 7400 Coins
Level 9: 8000 Coins
Level 10: 8600 Coins
Level 11: 9200 Coins
Level 12: 9800 Coins
Level 13: 10400 Coins
Level 14: 11200 Coins
Level 15: 11800 Coins
Level 16: 12400 Coins
Level 17: 13000 Coins
Level 18: 13600 Coins
Level 19: 14200 Coins
Level 20: 15000 Coins