The game has a maximum limit on the amount of silver and other currencies you can accumulate. This limit is necessary to ensure the system runs smoothly and to prevent errors related to how data is stored.
What is the limit?
The maximum amount of silver you can accumulate is 2,147,483,647.
This same limit applies to any other currencies or resources, unless otherwise specified.
What happens when the limit is reached?
When you reach this limit, any additional silver (as well as other affected currencies) that you attempt to earn will not be counted until your balance decreases.
In other words, if you continue playing without spending resources, you will stop receiving silver and other mission rewards.
How do I start earning currency again?
To resume earning silver and other rewards, simply spend some of your accumulated resources. You can do this in the following ways:
1) spend some of your available silver on upgrading heroes;
2) use silver in the shop to buy equipment;
3) spend silver on upgrading artifacts.
As soon as you spend enough resources to bring your balance below the limit, rewards will resume automatically.