Make feature tests frictionless to work on and run. They act as a form of documenting the system. Documentation which acts as a proof the system works the way its stated. This will help with iterating on the code base.
The feature tests need to be minimal, targeted, lowering their long term maintenance footprint.
Make it easier to iterate on the code and prevent regressions by improving payment integration testing.
Make sure the payment code is solid by improving unit test coverage. This helps discover bugs and prevents regressions.
Taler is a payment method whose currency is configurable. The system assumes a single currency, KUDOS. Extend the system to make it work any currency using Taler.
Golang's standard practice is to prefer returning references. Make sure this is followed almost consistently.
The way the templates are generated can be more intuitive. Simplify and clean up.
Describe how the system handles and records transactions, and importantly, why it is that way.
How are things setup, and why are they that way?
Describe operating the project from a maintainers perspective in a clear concise manner, likely within the project's README. Support this with rationale as to why its this way.