This is Rae from Shopify. Thanks for letting us know about this situation.
Before we dive into some troubleshooting, I wanted to mention that I moved your post onto a new thread here on the Community, as it described a different issue than the original thread you posted in. This way, if others are running into the same troubles as you, they will be able to easily locate your post and join our conversation here.
In terms of the error you're seeing when you click on your Instagram icon, I'm happy to help look into this further.
You mentioned you're using the appropriate URL, but I was hoping to clarify that on your end the URL looks like this: 'http://instagram.com/shopify'? Please note, your own Instagram account name should be added after the '/', rather than 'shopify'. You can confirm your URL matches this format by following these steps:
If the URL that's currently added here doesn't match the above format, just go ahead and change this and then click 'Save' in the top right hand corner.
If this doesn't resolve things, please reply back to me here with a link to your live site so that I can check this out from my end. In addition to this, feel free to let me know which theme you're using, as this might be part of the issue, too. You can find your theme name directly in your Shopify admin under 'Online store > Themes'.
I hope to hear back from you soon with an update on how this goes!