Ted here from Shopify, thanks for posting your query!
Normally when this error occurs, the system is not recognising either the phone number or postcode you've entered. If there is normally a space in your post code, I'd recommend making sure to add a space into this field. For your phone number, try leaving out the area code. For example, if you were based in Ireland; enter 0871234567 as opposed to +353871234567 or 00353831234567. If this fails, please try the area code with either the plus (+) sign or "00" in front as shown above for example.
Please let me know how this goes!