This app requires an update of your Forerunner 955 Solar. Please use Garmin Express to update your Forerunner 955 Solar.

Same with my brand new Forerunner 255 Music...

me neither. I also cannot log in the garmin connect iq on my iphone.  

If you are using the web to access the CIQ store, then try the suggestion from the article Connect IQ Content Installation Requires Software Update | Garmin Customer Support (clear the browser cache / temporary files). If you are using the mobile CIQ app, try clearing its cache, or reinstall it.

Also connect your watch over the USB cable to a computer with Garmin Express, and check with it for firmware updates (just like the first poster did).

Anyone fix this?  Brand new garman 955 and I can't get spotify on it.  Up to date on everything as far as I can tell.  Should I return this watch? Already diappointed. 

The solution that worked for me is to download the apps directly from the watch. Posting here incase others are stuck like I was. 

You’ll need to check if the ConnectIQ Store app is already installed on your device. I believe it might be by default, as mine was already there. 

I still receive the same error through the ConnectIQ app on my iPhone and the website. But through the watch version ConnectIQ Store app, I am able to browse and download successfully. And once the app or watch face in installed, I am able to manage the settings through the iPhone ConnectIQ app, even though that app still gives me the error.