In order for InterCompany to work, it needs the database user credentials of a superuser of the database server.
This is used to find SAP B1 databases on the server, run cross database queries and more.
Go to Administration à Add-Ons à B1 InterCompany à Database Information.
Enter user name and password for a database superuser.
On MSSQL this is usually set to the sa user and on HANA it is usually the SYSTEM user.
IMPORTANT: This has to be done in all databases in the InterCompany setup.