Hi
Can you please elaborate on the process of “Ship Order” and “Set As Fulfilled”
and what does the 2nd Image showing n"not ready to ship" this comes when we try to ship an order
Please clear these terms 
HI @khungersumit!
The Ship Order button there is deprecated, to be able to ship the order you will need to use either the Mobile app or go to shipping.shiphero.com
As for the difference between those two
Set as Fulfilled: is an option that will allow you to set the order as fulfilled and remove inventory if you want, but will not create a real label.
Ship Order: This one is to ship the order and create a real label for it
The error you are seeing there might be an allocation error, in Show Details you might see more information about that, it should point you to the SKU that is having the issue.
Let me know if that doesn’t help.
Thanks!
Tom