Usually, the object of an active sentence becomes the nominative subject in a passive sentence. However, when an Icelandic verb requires a dative (or genitive) object, that object keeps its original case when it becomes the subject of a passive sentence. This is known as an oblique subject.
Take the verb henda (to throw away), which takes a dative object:
In the passive voice, the noun gögnin (the data) stays in its dative form, gögnunum:
The Default Neuter Singular Participle
In a standard passive sentence, the past participle agrees with the nominative subject. Because an oblique passive has no nominative subject, it defaults to a fixed grammatical form. The auxiliary verb (like var) stays in the third-person singular, and the past participle locks into the neuter singular (usually ending in -t or -ð).
Notice how the past participles (svarað, lokað, læst) remain neuter singular, regardless of whether the dative subject is a feminine word like beiðninni (the request) or a masculine word like netþjóninum (the server):
Directing and Transferring
This pattern is very common in customer service and IT with verbs like vísa (to direct) or breyta (to change). Notice how the active dative object (viðskiptavininum) mirrors the passive dative subject pronoun honum (him):