A feature is not an outcome
The fact that a system can create an invoice or send a notification does not prove its value. You need to know what changed in the process: cycle time, number of manual actions and frequency of errors. Functionality is the means, not the success metric.
Choose a few operational indicators
Useful metrics include time from input to outcome, cost per operation, returns to an earlier stage and team capacity. For customer processes, add first-response time and the share of enquiries without a next action. You do not need dozens of metrics, only the ones connected to the original problem.
Compare similar periods
Record a baseline before launch, give the team time to adapt and measure again under a comparable workload. Track the reasons for exceptions separately. The standard route may become faster while complex cases still require further design.