Hey @Arena_N .
Thanks for reaching out.
I appreciate the screenshot that you have added as that is very helpful! Could you let me know which application you are wanting to install?
By any chance, could you attempt to clear the cache on your browser and try this action again? In some cases, clearing the cache on your browser can clear up mirror issues that you may experience with the Shopify admin.
If the issue persists, you can try to use a separate browser - for example, if this error message is happening when you are using Safari, try adding the application to your online store using Google Chrome.
Let me know if that does the trick.