This is quite a common issue for several people and and somehow logical as well.
The A2017G is sold worldwide and some countries receive individual interim versions related to regional requirements.
ZTE has IMEI databases for the regions.
But...several resellers sell into different countries. So the databases can never be 100% up to date.
So ZTE offers two solutions.
1. You can send your IMEI to the respective country service for OTA, what often works.
2. ZTE provides the full version download for everybody who still doesn't succeed.
In my opinion a good service, though it still could be improved a little.