Vouchers I earn are not being added to my Voucher balance

Each type of Voucher has a cap of 1000.

You cannot collect more Vouchers of that type from free actions like drops, watching ads, or rewards once you reach this limit. 

To collect more of the same type of Vouchers, try spending some first. The Luxury Market and Boosters are great places to use your Vouchers!

However, Vouchers obtained through in-game purchases will still be added to your balance, even if you already have 1000.