Shopify Shipping & Gateway Fixes

My Shopify store’s checkout is confusing customers and costing me sales. Domestic shipping is the biggest pain point right now—rates are wrong, the option I want sometimes disappears, and the custom rules I’ve set up never seem to trigger. On top of that, delivery-time estimates are off, several local zones are missing, and the courier app integration keeps throwing errors.

Here’s what I need from you:

• Diagnose and correct the rate-calculation logic so the numbers shown at checkout match my carrier tables.
• Make sure the preferred shipping method is always available and the custom shipping rules fire exactly as configured.
• Rebuild the domestic delivery setup: add all intended zones, show realistic delivery times, and restore a clean connection to the courier API.
• Review the payment gateway settings, run a test transaction, and confirm the entire order flow works without declines or unexpected fees.

I’ll provide full Shopify admin access, current carrier rate sheets, and any gateway credentials needed for sandbox testing. Once everything is stable, please document the changes so I can maintain them going forward.