We have a need for multiple credit buckets (wallets). In our offerings we collect $X / year from our customers of which a part is for the fixed fee and then the remaining is for the usage. So, there is fixed fee credits and then credits for usage . Every month we need to deduct say, $A from the fixed free credits bucket and say, $B from the credits for usage bucket. We cannot have the same bucket for both. Once the user runs out of credits for usage, they will start paying. In future we may have different wallets for different class of service as well (a simple example could be like paying a mobile operator for voice and data from different wallets). In the invoice we need to show what is deducted from each wallet every month. It would be ideal if the invoice could also include what the balance was at the start of the month and then at the end of the month! Let me know if this feasible and/or you have questions around this.