HELP: How to Test the TT-38 Decouplers at Launch Site

[Dying2PlayGames]

So, playing KSP. Still new, but cannot complete this stupid mission and I don't understand why! It says to test the decouplers at launch site, but even though my "Kerbin, Launch Site" notes are all green, only testing needed to complete. But when I stage the decoupler, it goes flying but it doesn't complete the mission. I tried using a scientist instead, right clicking on the decoupler instead of staging with spacebar, and there's no option to "TEST" anywhere. what DO I DO!!! Lol... 

[Vanamonde]

Do you have a screenshot of your test build? 

[DeadJohn]

Welcome and congrats on your 1st post.

Are you certain you are using the correct part? Maybe you just mistyped "TT-38" but the stock radial decoupler is "TT-38K".  If you installed mods maybe you have some similarly named parts.

Worst case, you can give up and cheat the contract complete. Open the debug window (alt-f12), click to active contracts on the left side, then click the button to complete the desired contract.

[Clayel]

Make sure you have a probe or capsule on the craft so you can control it