Magento 2.3.5 — Custom module: add-to-cart landing page for Meta Shops checkout links

Our store slballoontime.com runs Magento Open Source 2.3.5-p2 (Nexcess hosting). We sell through Facebook Shops with 'checkout on website'. Meta sends shoppers to our checkout URL with a query parameter listing the products, for example: https://slballoontime.com/checkout/?products=ACC-STUFF-MA-1SET:4,ACC-NET-500-DROP-1PC:2&cart_origin=meta_shops Magento ignores the parameter and redirects to an empty cart page, so Facebook Shop customers cannot buy. Job: Build a small custom module (no core edits) that: 1. Provides a landing route that reads the products parameter (format: SKU:qty, comma-separated; the IDs are our product SKUs, matching the Meta catalog retailer IDs). 2. Loads each product by SKU and adds it to the visitor's cart with the requested quantity (simple products; catalog items are simple/variant SKUs). 3. Redirects (302) to /checkout/ with the items in the cart. 4. Handles bad input gracefully: skip unknown or out-of-stock SKUs and still add the rest; if nothing is valid, redirect to the homepage — never an error page. 5. Does not change or break the normal cart/checkout flow in any way. Requirements: - Proven Magento 2 custom-module experience (please link one example module or integration you built). - Must work on Magento 2.3.5-p2 specifically. (Note: the official Meta extension requires 2.4 — that is why this is a custom job.) - Take a full backup before deploying; deploy in a short maintenance window we agree on. - Deliver the module as installable files with brief install/uninstall notes. Acceptance test (payment milestone): Opening the test link with 1 SKU lands on checkout with that item in the cart; a second test with 2 SKUs and quantities lands with both. After that, Meta Commerce Manager's checkout preview test must pass. Budget: Fixed price. This is a small, well-scoped job — please quote your fixed price and delivery time. Possible phase 2 (separate project, separate quote): auditing and repairing our Walmart Marketplace connection to this same Magento store — product/SKU mapping, price and inventory sync, and order import. If you have done this before, mention it in your proposal.