You either need to import the project as a Gradle project from within Idea. When you add a dependency you need to open the Gradle window and perform a refresh.

Alternatively generate the project files from gradle with this:

build.gradle:

apply plugin: 'idea'

And then run:

$ gradle idea

If you modify the dependencies you will need to rerun the above again.

As mentioned by @maheeka in the question's comments, if the project is a Maven project, the simplest way to achieve updating changed external libraries is to right-click on the project, and select Maven > Reload project.

You can actually see IntelliJ re-indexing the changed libraries individually during the operation in the bottom right status bar.

Tested on v2021.1 Ultimate.

I have run into some very sticky snapshots. There are a few options you can try:

• On the Gradle tab (right side of UI), click the blue circling arrows icon, which should refresh the dependencies (works in most cases)
• If that does not work, try running the gradle command in IntelliJ using the Green "run Gradle command" icon - this runs the command in IntelliJs environment not that of your local machine.
• If both of those fail, you can modify your Gradle resolutionStrategy settings to something like: configurations.all { resolutionStrategy.cacheDynamicVersionsFor 4, 'hours' resolutionStrategy.cacheChangingModulesFor 4, 'hours' } This config change is a last-ditch option and should be used sparingly. It basically tells Gradle to refresh the local cache more often. You should click the IntelliJ Gradle refresh button after making these changes.