2005 Highlander V6 for Oil and Transmission Fluid Change Leaking Issue on 2005 Toyota Highlander

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
I just recently have it service my 2005 Highlander V6 for Oil and transmission fluid change including 50k and multipoint inspection. After 3 weeks, I noticed it from the driveway there were spots; somewhere leaking underneath the car. I checked below the engine, I saw an oil leak. Please let me know what was the cause of it....and an immediate repair to solve the issue. (Mileage: 70,000) tnx.
(2) Answers
Need to find exact location. Most likely suspects: Check oil plug and see if the gasket is on it (Not all vehicles have a gasket on them) Next, oil pan gasket could have failed and need replaced. Have to find location of leak to be sure.
go back to where you had service done at, it should be still under warranty, be as specific as possible in telling the repair shop what you see, when, and how often you notice the leakage.