It's tough to tell what's going on here but typically when an error message like this appears, there could be multiple addresses on a store.
I'd love to dig into this further with you to find out what's happening.
Here are some questions to troubleshoot: What is the name of the app that you're trying to download?
Where are you trying to add your address?
Do you have a screenshot of the error?
Once I hear from you, I'll be able to assist!
Tira | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog