(Retrofit) Could not locate converter for class crashing app

I was facing the same issue. I fixed it by adding :

compile 'com.squareup.retrofit2:converter-gson:<latest-version>'

to my build.gradle

Then specify the converter when creating my Retrofit instance.

Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(Constants.API_BASE_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .build();

In Retrofit 2.0, Converter is not included in the package and when you are using Retrofit 2.0 Make Sure follow new URL pattern

Base URL: always ends with /

@Url: DO NOT start with /

Retrofit retrofit = new Retrofit.Builder()
        .baseUrl(Constants.API_BASE_URL)
        .addConverterFactory(GsonConverterFactory.create())
        .build();

For more information about 2.0 Follow this link Retrofit 2.0: The biggest update

And also update build.gradle.

implementation "com.squareup.retrofit2:converter-gson:$retrofit_version"

And add the extension in project level build.gradle file

ext {
retrofit_version= "2.x.x"
}