Overage billing automation for custom module product

[johnc]

Hello guys,

I looked up community site and WHMCS documentation, but could not solve my problem.

I already read these docs.
https://docs.whmcs.com/Disk_Space_and_Bandwidth_Overage_Billing
https://developers.whmcs.com/provisioning-modules/usage-update/

Could you let me know how I can solve this ?

Case is like the following,

```
custom_provisioning_module - talk to a server
foo_product (pro-rata, service can start any day )
  - custom_provisioning_module (assigned)
  - configurable options [DATA]
    - 100GB($50)
    - 500GB($70)
    
    excess data charge $1/GB

A customer purchased foo_product, service period(16/Mar/2018 ~ 15/Apr/2018)
A customer used 150GB(150-100=50GB excess) until 15/Apr/2018
```
How can I update invoice for overage billing automation ?
Please let me know what the best practice is.