Node.js API Bug Fixes Needed -- 2

My current Node.js backend has a handful of existing APIs that require some fixes and 2-3 new apis it's using atlas(mongodb) as database .I need the underlying issues identified and resolved so each route responds quickly, handles errors gracefully, and passes regression tests before we push the next release. Tech stack in place: Node.js 18, Express 4, MongoDB using Mongoose. If you prefer additional debugging tools such as nodemon, ESLint, or Postman collections, feel free to incorporate them. This is a focused repair job rather than a full rewrite. Most fixes should be straightforward once the root cause is found, but I value clean code and thorough testing. Let me know your estimated turnaround and any clarifying questions you need answered before diving in.

Project ID: 40432324