Download of add on Relics of the Skies not working

Relics of the Skies has been purchased with gold and the download can be started, but is not finishing succesfully.

The Imagiverse support has forwarded me to Xbox Support but they could not help. Checking and resetting everything together with the Xbox phone support did not change the behaviour.

My kids have collected their money to buy this and now wait for many days to get something for theim money. Please help.

I have added screenshots to my original post, but I did not know that English is required for error reports.

https://bugs.mojang.com/secure/attachment/180361/20180819_133254.jpg

https://bugs.mojang.com/secure/attachment/180360/20180819_133348.jpg