Hi @Manuel
The search via API works exactly the same as via the UI. See this help page for examples. Especially the AND and OR options might be useful.
GET https://www.my-zammad.com/api/v1/tickets/search?query=alarmkey: %20IF_DOWN_0x00008391_35
The URL parameter is as follows:
query=[object]: [value]
You need to url-encode your query. So the space becomes %20. : will work but you can also use %3A. Or just use https://www.urlencoder.org/