How to ensure quality checks and errors on fields and operations?

Question

Validation

Subject, weak team. Lots of johns. Almost all tasks without field checks, without displaying errors (for example, you did not fill in the *** field). How to ensure quality in terms of PM? Instructing a developer to personally dig for best practices for errors and validations is unproductive to waste a lot of time. Search yourself and create tasks? So far the most productive solution, because there are a couple of windows at a few hours. But where to look?
Need help and advice.