Unable to resolve firebase 17.0.4

Hi DW, I'm experiencing an issue I've tried invalidating, fixed the offline sync but still I'm getting this error. My App uses Firebase FCM.

On the dependencies I have com.google.firebase:firebase-core:16.0.5 com.google.firebase:firebase-messaging:17.3.4

My implementation com.android.support:appcompact-v7:28.0.0-alpha1

This implementation is underlined with a red line and I think it is what having the issue, i remember now when I had this kind of error before I saw a post that said I must change the version here but don't know to which version to change to. If anyone know how can I fix this error please help me out. Thanks