Petpooja POS Stock Discrepancy Tool

We currently use Petpooja POS, and I want to eliminate manual sales entry to find daily stock discrepancies (thrift/loss).
The Workflow
1. Opening Stock: Should automatically pull from the previous day's "Closing Stock."
2. Manager Input (Daily): A simple interface (form/sheet) for the manager to enter Production quantities.
3. Petpooja Sync (Daily): The system must use the Petpooja API to fetch the quantity of items sold for that specific day.
4. Staff Input (Nightly): A simple interface for the salesperson to enter the Physical Closing Stock found on the shelf.
5. Auto-Calculation: The system must calculate the "Expected Stock" and compare it to "Actual Stock."
Key Deliverable: The "Plus or Minus" Summary
The final dashboard must show a single financial figure:

Total Daily Variance = (Expected Stock - Actual Stock) × MRP.
I need to see if the total sum is (+) or (-) at a glance to identify theft or wastage.

Technical Requirements
• Experience with Petpooja API (v2.1.0 or latest).
• Ability to create a user-friendly input interface (Google AppSheet, Retool, or a simple Web Form).
• Automation of data fetching (e.g., via Google Apps Script or Python/Zapier).
• Expertise in logic/formula building for inventory tracking.