Hi @zhaush ,
Perhaps you can take a look at Order Fulfillment Guru? You can automatically route specific products in an order to your supplier. It automatically handles order splitting as well - if an order contains items that needs to be fulfilled by your store and by your supplier, it automatically splits it as well. Let me know if you have any specific questions.
@Claire222 I'm not sure your role in the company or if you're aware but your team was caught leaving fake 5 star reviews on your app listing, and fake 1 star reviews on other fulfillment app listings (multiple apps were attacked). Reference: https://speedboostr.com/shopify-partners-caught-stealing/#copyright-cork
This is unethical, probably illegal, a breach of Shopify terms of service, and speaks negatively to the character of your company (they cannot be trusted). This type of malicious behavior is a big red flag for Shopify store owners that trust apps to use their data responsibly.