Python WhatsApp Rent Reminder Bot

I have a Google Sheet that holds our tenant roster (name, WhatsApp number, unit, rent amount, due date, payment status). I want a Python-built bot that polls this sheet every day and, based on the status column, automatically pushes personalised WhatsApp reminders:

• 1st reminder on the 7th
• 2nd reminder on the 14th
• Final reminder on the 31st

Only tenants still marked “unpaid” should receive a message that clearly states their outstanding amount and due date. I also need a simple command-line or webhook-style endpoint that lets me resend a reminder to any single number on demand.

Key preferences
– Language: Python.
– WhatsApp delivery: a 3rd-party gateway that is not the Meta Business API; feel free to suggest Twilio, Vonage or another cost-effective option that can be self-hosted or run on a small VPS.
– Error strategy: if the Sheet contains incomplete or malformed data, just log the problem and keep processing the rest.

Architecture constraints
No Zapier, Make.com or other paid middleware. I’m looking for a lightweight, self-hosted solution (Flask/FastAPI + cron, Cloud Functions, or a Dockerised microservice—your call). Please outline the stack you plan to use when you reply.

Deliverables
1. Fully working bot with source code.
2. Brief README covering setup, environment variables, and how to trigger the manual resend.
3. Short hand-over call or screen-share so I can see it in action.

If you’ve built anything similar—especially WhatsApp or Google Sheets integrations—include a link or short summary. I’ll prioritise applicants who can point to live examples and who offer a clear plan for hosting and ongoing maintenance.