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