Vouchers are handled by specific orders in OpenCart. In your admin - > sales - > orders page, you can track vouchers by selecting a specific order. Although, if you're referring to a report module to where all vouchers would be displayed with their statuses like sales reports. for instance, this feature is not integrated in the core. I would suggest to look for an extension that might provide your request from the extensions site or to request to feature to be done as a custom job in the commercial support section of the forum.
The most generated errors being found on Opencart forum originates from contributed programming. The increased post counters are caused by redundancies of the same solutions that were already provided prior.
Opencart.com Administrator / Quality Assurance Analyst / Programmer