It may not be possible to save the configuration file Apsis.Service.exe.config after having specified the Apsis account details. This is due to the fact that Windows protects files in C:\Program Files (x86) and requires administrator access to change data there. Open e.g. Notepad as Administrator (right-click, Run as administrator) and open the file as a workaround.
Verbose logging output is always enabled and ends up in C:\ProgramData\Lundalogik\Apsis Integration\debuglog.txt. If things don't seem to work it is always a good idea to have a look in this file for a possible explanation.