funktionierend
functioning
In a state in which something works as it should; intact and ready for use.
Wir brauchen eine funktionierende Heizung, bevor der Winter kommt.
We need a functioning heating system before winter comes.

functioning
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functioning
In a state in which something works as it should; intact and ready for use.
Wir brauchen eine funktionierende Heizung, bevor der Winter kommt.
We need a functioning heating system before winter comes.

'Funktionierend' (functioning) is the present participle of the verb 'funktionieren' (to function / to work). It is used like a normal adjective and declined before a noun.
Ein funktionierendes Team ist der Schlüssel zum Erfolg.
A functioning team is the key to success.
This adjective is almost always used attributively, that is, directly before a noun. Predicative use, e.g. 'Die Heizung ist funktionierend.' (The heating is functioning), is rare and sounds unnatural.
Ich suche ein altes, aber noch funktionierendes Radio.
I'm looking for an old but still functioning radio.
In the technical meaning, it describes devices and machines. Typical combinations are 'eine funktionierende Bremse' (a functioning brake), 'ein funktionierendes Gerät' (a functioning device), or 'ein funktionierendes Netzwerk' (a functioning network).
Ohne eine funktionierende Kaffeemaschine fängt der Tag schlecht an.
Without a functioning coffee machine, the day gets off to a bad start.
In the figurative meaning, it describes complex systems. Common combinations are 'eine funktionierende Wirtschaft' (a functioning economy), 'eine funktionierende Gesellschaft' (a functioning society), or 'eine funktionierende Partnerschaft' (a functioning partnership).
Eine offene Kommunikation ist die Basis für eine funktionierende Beziehung.
Open communication is the basis for a functioning relationship.
active
'aktiv' and 'funktionierend' can both say that something is not off or not broken. 'aktiv' emphasizes that something is switched on, effective, or currently in operation. 'funktionierend' emphasizes that something is working properly and does not have any major problems. An account can be 'aktiv' even if you are not using it at the moment. A device is 'funktionierend' if it does what it is supposed to do. For people, 'aktiv' fits for energy or engagement, while 'funktionierend' is more for things, systems, or processes.

Für die Präsentation brauchen wir einen funktionierenden Beamer.
For the presentation, we need a functioning projector.
Das alte Benutzerkonto ist noch aktiv, obwohl Max es kaum nutzt.
The old user account is still active, although Max hardly uses it.