1. A concise explanation of the problem you're experiencing.
I am unable to upload a gltf model version 2.0.

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.
An error occurred while rendering. Rendering has stopped.
RuntimeError: Unsupported glTF Extension: KHR_technique_webgl
    at new RuntimeError (http://localhost:8080/Source/Core/RuntimeError.js:42:19)
    at Object.ModelUtility.checkSupportedExtensions (http://localhost:8080/Source/Scene/ModelUtility.js:504:27)
    at Model.update (http://localhost:8080/Source/Scene/Model.js:4383:34)
    at PrimitiveCollection.update (http://localhost:8080/Source/Scene/PrimitiveCollection.js:369:27)
    at updateAndRenderPrimitives (http://localhost:8080/Source/Scene/Scene.js:2939:27)
    at executeCommandsInViewport (http://localhost:8080/Source/Scene/Scene.js:2778:13)
    at updateAndExecuteCommands (http://localhost:8080/Source/Scene/Scene.js:2586:13)
    at render (http://localhost:8080/Source/Scene/Scene.js:3226:9)
    at tryAndCatchError (http://localhost:8080/Source/Scene/Scene.js:3246:13)
    at Scene.render (http://localhost:8080/Source/Scene/Scene.js:3295:13)

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you're using, your operating system and browser.
Cesium 1.54. MacOS. Chrome

This extension was renamed at some point, see the thread here:

You should be able to re-convert it using the latest obj2gltf and get a correct model.

Thank you Omar but I do not have the obj file I only have the gltf to work with you know if I can use the obj2gltf to convert a gltf file?