Shopify Plus Expert for Shipping Fix

We operate a Shopify Plus store selling commercial HVAC replacement parts to both retail and wholesale customers across the U.S. and Canada. Our setup includes: - Shopify Plus with B2B company accounts and customer-specific catalogs - Shopify Markets for U.S. and Canadian customers - Three fulfillment locations: our warehouse, a third-party logistics provider, and a dropship supplier - Separate shipping profiles for stocked, oversized, and dropship products - Carrier-calculated UPS and FedEx rates - A custom Shopify Function for wholesale pricing and quantity rules After connecting a new 3PL location and updating our shipping profiles, certain customers started receiving the following message at checkout: "This order can't be shipped to the address you entered." The problem appears primarily when a cart contains products assigned to different fulfillment locations. Orders containing products from only one location usually work. Logged-in B2B customers are affected more frequently, although we have reproduced the issue with some retail orders as well. We need someone who can join a live screen-sharing call immediately, inspect the configuration and relevant logs, identify the root cause, and help us resolve the issue during the call if possible. You should be comfortable troubleshooting: - Shopify multi-location inventory and fulfillment routing - Shipping profiles and delivery profile conflicts - Carrier-calculated rate aggregation - B2B company locations and market-specific shipping rules - 3PL or fulfillment-service location configuration - Shopify Functions and checkout validation - Admin API or GraphQL inspection when the Shopify admin does not expose enough detail This is an active production issue affecting paid traffic and wholesale orders, so availability right now is essential. Please apply only if you can: 1. Join a live call within the next 30 minutes. 2. Personally troubleshoot the issue during the call. 3. Show that you have resolved a closely comparable Shopify multi-location or mixed-cart shipping failure before. In your response, begin with: "Right now". Then briefly explain the closest comparable issue you handled and what caused it.