I've successfully registered an on-premise PostgreSQL Database within ArcGIS Server. I've also been able to establish a database connection to an off premise PostgreSQL Database and can read and write data on this database.
Now, I'm trying to register the very same (off-premise) PostgreSQL Database on the ArcGIS Server. To make sure that my input is 100% correct, I import the the database connection (.sde) that I previously successfully established. But when registering the database, I get the following error: