Set up flat shipping rate for multi shipping origins

[Merakidea]

I have a problem with the flat rate shipping setup for multi shipping origins. I want to set up a flat rate for the order placed by the customer. However, products are shipped from more than shipping origins and the issue is when the customer adds products shipped from 2 shipping origins, he/she is charged with shipping origins combined at checkout. 
I'm wondering if there's any solution to set up a flat rate for the order.

Thank you.

[MiraPatil]

Hello @Merakidea 

Can you please check out with Shipping & Delivery ‑ ShipZip ?

It has option to set a single delivery charge(a flat rate) if order comes from multiple locations. 

Easy to setup on the app to create a zone, and a rate with base price and set a single location fee option on the setting page.

App support provides live chat to help you shipping rates. 

Also available to test free in test mode. 

Just for information: You should have enabled CCS(custom carrier service) on your store to set shipping rates from third party APP. (that comes free with height or advance plan OR annual billing cycle with shopify($79) plan.