Before clicking Connect, an admin needs to do these once in Google Cloud Console for the project tied to GOOGLE_CLIENT_ID:

1. Enable the Google Business Profile APIs. APIs & Services → Library → enable: My Business Account Management API, My Business Business Information API, My Business Q&A API.
2. (Optional first; required if API calls 403) Try connecting + linking a client first. Sometimes the GBP API works immediately when the connecting Google account already owns/manages the locations. If it does, skip this step. If API calls return "PERMISSION_DENIED" or "This API is disabled for your project", you need allowlisting:
   • Visit Google's current Business Profile API prereqs page — it links to the live access-request form (Google has moved this URL several times; their docs always have the current one).
   • Or open support.google.com/business/contact/api_default as a fallback.
   • Approval is typically 1–3 business days. Submit it now even before testing — the form just asks for your GCP Project ID + a brief use-case description.
3. Configure OAuth consent screen. APIs & Services → OAuth consent screen → fill app name + support email + add the .../auth/business.manage scope. While the app is in "Testing" mode, every team member who'll connect must be added under Test users.
4. Register this redirect URI exactly under APIs & Services → Credentials → your OAuth 2.0 Client → Authorized redirect URIs:
   Copy
   A "redirect_uri_mismatch" error after clicking Connect means this URI isn't registered or has a typo.

Once all four are done, click Connect Agency GBP Account. The flow opens Google's consent screen, you authorize, and you're redirected back here. After connect, the per-client Link to location button appears.