Are you trying to use a custom Java API. If so - you need to wrap that JAR that exposes the Java package into an OSSi bundle and deploy to AEM. Remember that when building an OSGi bundle that contains a Java API - you need to ensure 2 things:
1 - you reference the API in the POM (which you did)
2 - you need to make sure there is a deployed OSGi bundle in the AEM Service container that exposes the given Java package - sounds like this is not the case).