As described in this blog, there has been a change in API to access data stored in BIM 360 Docs in European data center. If you have customers in Europe, you most likely want to test your apps in European environment. (Please note that BIM 360 Docs in European region may have limited features compared with the version that is hosted in U.S. data center as typically new features are released in the U.S. first.)
If you wish to have a test environment in European region, please request for a free BIM 360 Docs account as below.