Gradle could not resolve project :linkedin-sdk

Since you are using the new android plugin 3.x you have to follow the migration guidelines:

Error:Failed to resolve: Could not resolve project :linkedin-sdk.

To resolve this error, you need to specify which build type from “mylibrary” (linkedin-sdk in your case) the Android plugin should match to the app’s “staging” build type. You can do this with the buildTypeMatching property in the app’s build.gradle file, as shown below:

android {
    ...
    // Tells the Android plugin to use a library's 'debug' build type
    // when a 'staging' build type is not available. You can include
    // additional build types, and the plugin matches 'staging' to the
    // first build type it finds from the one's you specify. That is,
    // if 'mylibrary' doesn't include a 'debug' build type either, the
    // plugin matches 'staging' with the producer's 'release' build type.
    buildTypeMatching 'staging', 'debug', 'release'
}

Edit:
buildTypeMatching was replaced by matchingFallbacks.
You can find more info about the variant-aware dependency management
here and here.

android {
    buildTypes {
        debug {}
        release {}
        staging {
            // Specifies a sorted list of fallback build types that the
            // plugin should try to use when a dependency does not include a
            // "staging" build type. You may specify as many fallbacks as you
            // like, and the plugin selects the first build type that's
            // available in the dependency.
            matchingFallbacks = ['debug', 'qa', 'release']
        }
    }
}

Then

Unable to find a matching configuration of project :linkedin-sdk:

You can use

compile project(path: ':linkedin-sdk', configuration: 'default')

but you can simply use the following to take advantage of variant-aware dependency resolution. .

implementation project(':linkedin-sdk')

You can learn more about the 'implementation' configuration in the section about new dependency configurations.