Bad news and good news about your xml...
Bad news: The file in your .zip has a non-standard format that OOTP can't read due to the use of Excel to edit it.
Good news: If you open it in Excel, and copy the whole file into a text editor (I used Notepad++ for my doings, you'll find it at
https://notepad-plus-plus.org/download [shameless plug, I know]), and save the .xml file there, it will read properly.
Bad news: There are some minor errors that OOTP is having errors parsing.
Good news: It's (mostly) only because of missing </STATE> flags. These states have them:
1. Vesta
2. Hygiea
3. Harmony One
4. Nolan Station
5. Ganymede
6. Europa
There is also a region error that shows up with Venus; a <REGION_NATIONS> flag is missing at the beginning (there is a proper ending for it, however...)
Does this make sense? I'm no expert, but world editing/building is an area I enjoy working with, and those things are what I saw from first glance and did from first tinkering with your .xml file.
Anyway, make those little adjustments, and you can rep the Apollos proudly.
Let me know if it works out for you.