You have a minimum viable product or high fidelity prototype. Your venture is lucky enough to attract first customers. The problem is that your software product lacks the main feature – stability. This might spoil the opportunity.
You can perform manual testing. Usually regression manual tests are time consuming and cost much. Also they slow down time for features to reach your first early customers.
Better solution is to cover the software product with automated testing. You can also perform manual testing, but smaller amount. Ideally all repetitive manual test cases should be automated.
We did exactly this job for our client Inno-w Oy. Finnish company that actively develops online services. Software is mainly produced within Ruby on rails stack of technologies.
Added shell scripts to github that automatically do all settings described in slides.
Testify Rails scripts