Figured it out on my end.
I added a new location to ship from, but hadn't set up the shipping rates for the location specifically.
So, I clicked on settings > locations and then at the bottom, chose the second location, and clicked copy from this profile.
It works now! Customers can place orders again!
Yes I also ordered a water heater fromhere and they sent me the same message ordered so many things before with the same order but this time they are not approving my address what is the reason please guide me.