Could not resolve all files for configuration ':app:debugRuntimeClasspath'.

This error message indicates that there is a problem with resolving dependencies for your project's runtime classpath in debug mode. There could be several reasons for this issue, including:

1. Network connectivity issues: Check if you have a stable internet connection and try syncing the project again.

2. Gradle cache corruption: Try deleting the Gradle cache directory and syncing the project again.

3. Incorrect dependency configuration: Verify that you have added all the necessary dependencies in the correct format in your project.

4. Gradle version compatibility: Ensure that your project's Gradle version is compatible with the dependencies you are using.

5. Incorrect project structure: Check if your project structure is correct and all necessary files are in the correct location.

You can also try running the "clean" command to clean your project and rebuild it. If the issue persists, you may need to provide more information about your project setup for further assistance.