The extension won't install either in my production tenant or in the sandbox. In the sandbox, the "Extension Deployment Status" action isn't enabled. This action is enabled in the Production tenant, so I can see a status of "failed".
When I click on "Deploying Extension 7e6a25d2-46d1-49a1-9b76-9e05b11204ea", I get a summary of "The extension failed to be deployed successfully. View the error details for more information and then deploy again."
When I click on "View Details", I get an explanation of "Deployment failed. Errors: App ID : 7e6a25d2-46d1-49a1-9b76-9e05b11204ea Message : { The extension is not available for your release. Check the country and version availability in the extension marketplace. } - Job Id : d81b7b8a-973d-4ae7-90bd-a12c6d82adab".
I am installing in the US. My build in production is "US Dynamics NAV 13.1 (26678)". My build in the sandbox is "US Dynamics NAV 13.1 (26534)".
It really couldn't get much more vanilla than this, so I don't see why this is causing a problem...