Cannot call helper methods

I am trying to call helper methods defined in my API for the failure and success response. But am getting the not defined error. If I use the method defined inside the resource, it works perfectly. Is there no way to use the helper methods?

The below code throws the error

resource :users do
    desc "User Authentication API",
        summary: "This is the API used to authenticate the user"
        failure: [ invalid_login_credentials_error ],
        success: sign_in_successful_msg
    post :sign_in do
    ....
end

helpers do
    ....
    def invalid_login_credentials_error
        { code: 422, message: "Invalid email or password" }
    end
    ....
end

But the below one works perfectly

resource :users do

    def invalid_login_credentials_error
        { code: 422, message: "Invalid email or password" }
    end

    desc "User Authentication API",
        summary: "This is the API used to authenticate the user"
        failure: [ invalid_login_credentials_error ],
        success: sign_in_successful_msg
    post :sign_in do
    ....
end

Start by reproducing the helper lookup with the two snippets in the issue and trace how the failure and success values in desc are resolved. Identify the relevant API documentation entry point and add or update coverage for helpers defined in the API; done means the helper-based declarations behave consistently with methods defined inside the resource.