incrby method
Increments the number stored at key by increment. If the key does not exist, it is set to 0 before performing the operation. An error is returned if the key contains a value of the wrong type or contains a string that can not be represented as integer. This operation is limited to 64 bit signed integers.
See incr for extra information on increment/ decrement operations.
Returns he value of key after the increment.
Implementation
Future<int> incrby(String key, int increment) async {
return (await tier1.incrby(key, increment)).toInteger().payload;
}