I know that the credential is valid and that the APIs are correctly enabled because I can pull data fine using this credential, just not with this Meltano tap 😕 This script runs fine and outputs data:

from apiclient.discovery import build
from oauth2client.service_account import ServiceAccountCredentials

import json


SCOPES = [
    '<https://www.googleapis.com/auth/analytics.readonly>'
]
KEY_FILE_LOCATION = 'src/client_secrets.json'
VIEW_ID = '<my view ID>'


def initialize_analyticsreporting():
    credentials = ServiceAccountCredentials.from_json_keyfile_name(
        KEY_FILE_LOCATION,
        SCOPES
    )

    return build('analyticsreporting', 'v4', credentials=credentials)


def get_report(analytics):
    return analytics.reports().batchGet(
        body={
            'reportRequests': [
                {
                    'viewId': VIEW_ID,
                    'dateRanges': [
                        {
                            'startDate': '3daysAgo',
                            'endDate': 'today',
                        },
                    ],
                    'metrics': [
                        { 'expression': 'ga:users', },
                        { 'expression': 'ga:newUsers', },
                    ],
                    'dimensions': [
                        { 'name': 'ga:date', },
                    ],
                },
                {
                    'viewId': VIEW_ID,
                    'dateRanges': [
                        {
                            'startDate': '3daysAgo',
                            'endDate': 'today',
                        },
                    ],
                    'metrics': [
                        { 'expression': 'ga:sessions', },
                        { 'expression': 'ga:sessionsPerUser', },
                        { 'expression': 'ga:avgSessionDuration', },
                    ],
                    'dimensions': [
                        { 'name': 'ga:date', },
                        { 'name': 'ga:country', },
                    ],
                },
            ],
        }
    ).execute()


def print_response(response):
    print(json.dumps(response, indent=2))


if __name__ == '__main__':
    analytics = initialize_analyticsreporting()
    response = get_report(analytics)
    print_response(response)