Hi there @adhikary420!
Don here from Shopify.
I appreciate you taking the time to share your query here in the Shopify community.
There are a couple of ways you can approach this requirement.
Alternatively, you might be able to set your shipping rates in such a way that there is no rate available for orders where the price is less than 300 for eg.
This would mean your lowest available shipping rate would be for orders costing 300 and upwards, with no rates available that would cover smaller orders.
If you want to check this option out, it might be a good idea to leave a message somewhere in your store letting customers know about your minimum order requirements.
Are you currently using manual, price-based rates for your shipping, or something else?
How central would you say this requirement is to your specific business needs?
Let me know how I can help further in any case!