POS Go error "the store does not support the unit at this time"

[thfinch]

We are trying to add POS to our Shopify website. Subscription is POS Pro. We can process a POS transaction on a smart phone with the POS app, no problem. But when we try to connect a POS Go device, we get the message "the store does not support the unit at this time". 

And yes, the Store is in USA; we have Shopify Payments; retail location is in USA; and, we have a WPA2 wi-fi network.

This was all explained to support four days ago. While the estimated reply time was 24 hours, I haven't heard back. I followed up myself with support after 2 days, and was advised that I already was notified that support is following up on resolution.

In the meantime, has someone else experienced this? I cannot find any search engine results for this particular issue.