PayPal & Stripe WordPress custom Plugin

I’m building a WordPress site that needs its own e-commerce layer, so I want a custom plugin that handles two things flawlessly: taking payments through PayPal and Stripe, and keeping track of product inventory inside the WordPress dashboard.

The plugin should create a clean settings page where I can drop in API keys for both gateways, choose currency, and toggle test/live modes. On the front end it must expose a simple checkout flow—shortcode or Gutenberg block is fine—capable of single-product or cart-style transactions. Behind the scenes, stock levels have to update automatically when an order is completed, with low-stock email alerts and a manual adjustment screen for admins. No reliance on WooCommerce or other heavy frameworks; I’m after lean, well-documented code that follows WordPress coding standards and is ready for future hooks or filters if we decide to extend it.

Deliverables
• Fully functional plugin ZIP installable on any WP 6.x site
• Admin settings page for PayPal and Stripe credentials, currency, and webhook setup
• Front-end checkout form/block with success & error messaging
• Inventory management screens and automatic stock deduction
• Clear README covering installation, usage, and filter/action references

Acceptance criteria
1. Successful test transactions on both gateways using sandbox keys
2. Orders appear in a custom post type with payment and stock data attached
3. Stock decrements correctly and triggers low-stock email at the threshold I set
4. Code passes WP_DEBUG with no notices and meets PHPCS WordPress-Coding-Standards

If you’ve shipped similar payment or inventory plugins before, share a link or brief overview in your bid.