I found out what was wrong with my store in this regard.
I recently added new products to the store that were weighed or measured in oz or ounces, and I forgot that my product weight in the shipping zones , which is connected to the store is measured in grams. The new products were imported in oz or ounces, which meant that the shipping zone could not recognise or pick them up when my customers tried to pay for them.
Step 1: You need to go to products.
Step 2:Search and select the products you might be having issues with.
Step 3: After selecting the product, click on editing.
Step 4: Under 'Add fields' select weight and make sure that the weight your products are measured in here correlate with what you saved them as in the shipping zone.
I hope this helped
Ok so I just had this problem and tried all of the suggestions and it still didn't work. After contacting shopify and having someone look at my store I fixed it.
After making sure that your default location is set to an address your chosen courier or Aust post will ship from (under settings>locations), mine was originally set as my PO Box, so I changed to my warehouse address as you can't schedule pick ups for a PO box (obviously!). You then need to go into each product and make sure the location of the product is set to the correct location. Go into a product, scroll down to 'inventory,' select 'edit locations' and select the correct location. You will need to update your inventory as well, when you switch the product location it deletes your stock levels.
You can do this by selecting 'inventory' under the products menu on the left hand side of the screen, you need to make sure you have changed the default location on the products before you can do this.
Hope this helps someone!!
Hii, i was facing the same issue today. So someone guided me that the issue was cause by the weight of the products, for example i had set the custom shipping rates till 2.5kg to united kingdom , but my client was ordering items which exceeded the 2.5kg weight so she was seeing this error. As soon as i fixed this weight problem, she stopped seeing this error. So try it out. Hope it helps.