Code Review
Code review this entire feature. Find all bugs and issues.
Be highly skeptical about the code written, examine line by line, logic by logic. Identify redundant code, bad code, wrong logic, etc. — any and all bugs. Trace the call stack of each logic, until you've examined everything.
List all bugs and issues. Then, fix all issues found to ensure 100% working and no bugs and clean code.
Use verifiers and check for issues. Fix any. Ensure 100%.
Give TLDR.