I have designed and implemented several billing mechanisms.
Including designs/models orientated around licensing, another using AWS MMS (metering service) for the AWS QuickStart and more recently, one to capture product usage based on a specific frequency. The later architectured and delivered once again via serverless technology.
Created web apps [some serverless] to provide visibility into usage
Create application features to help mitigate restrictions on internet access
Subscription models designed and developed for: per agent, per user, per period, per feature usage, per role