Je préfère écrire dans la messagerie quand mon micro ne fonctionne pas.

Both are possible, but they don’t mean exactly the same thing.

• J’aime écrire dans la messagerie = I like writing in the chat (it’s something I enjoy).
• Je préfère écrire dans la messagerie = I prefer writing in the chat (I like it more than some other option, here: speaking with the mic).

So préférer + infinitive explicitly expresses a preference between options, usually A plutôt que B:

• Je préfère écrire dans la messagerie [plutôt que parler].
  I prefer writing in the chat [rather than speaking].

This is mostly a matter of French usage with specific nouns.

• dans la messagerie literally means “in the messaging system / in the inbox / in the chat area.”
• French often uses dans with places/containers (both physical and virtual):
  
  • dans le chat, dans la conversation, dans le document, dans le formulaire.

Sur la messagerie would sound more like “on top of the messaging system” and is not idiomatic here.
À la messagerie would sound wrong: we don’t “write at the messaging app.”

Other natural alternatives:

• Je préfère écrire dans le chat quand…
• Je préfère écrire par message quand…

La messagerie is a general word meaning “messaging system” or “message service.” Its exact meaning depends on context:

• On a video call (Zoom, Teams, etc.), la messagerie usually means the chat box.
• For phones, la messagerie vocale = voicemail.
• For email, la messagerie can mean the email service or inbox.

In this sentence, with the context of a microphone not working, la messagerie clearly means the chat (text box) in the call platform.

Grammatically:

• messagerie is feminine: la messagerie
• plural: les messageries (rare in this sense)

Both are possible, but they’re not identical:

• quand = “when(ever)” → refers to situations that actually happen or are expected to happen regularly.

  • Je préfère écrire dans la messagerie quand mon micro ne fonctionne pas.
    Whenever my mic doesn’t work (and this does happen), I prefer to write in the chat.

• si = “if” → introduces a condition, more hypothetical or uncertain.

  • Je préférerai écrire dans la messagerie si mon micro ne fonctionne pas.
    I will prefer to write in the chat if my mic doesn’t work (not sure if it will).

In your original sentence, quand suggests it’s a recurring or real situation, not just a theoretical one.

French uses the present tense for:

1. General truths / habits / preferences

   • Je préfère écrire dans la messagerie = I (generally) prefer writing in the chat.

2. Time clauses with quand expressing a general, repeated situation

   • quand mon micro ne fonctionne pas = when my mic doesn’t work (whenever that happens).

This is very similar to English “I prefer X when Y happens,” where both verbs are in the present.

Both mean “doesn’t work,” but there’s a nuance:

• ne fonctionne pas

  • Slightly more neutral/technical.
  • Often used with devices, systems, software:
    
    • Mon micro ne fonctionne pas.
    • Le wifi ne fonctionne pas.

• ne marche pas

  • More informal, everyday speech.
  • Also widely used with devices and things in general:
    
    • Mon micro ne marche pas.
    • Ça ne marche pas. = It doesn’t work.

In spoken French, people very often say:

• Mon micro marche pas. (dropping ne, very common in speech)

French usually uses a possessive adjective (mon/ma/mes) when English uses my:

• mon micro = my microphone
• le micro = the microphone (more general, not clearly belonging to anyone)

Here you’re talking about your own microphone, so mon micro is natural.

Reminder:

• micro is masculine: un micro, le micro, mon micro.

Yes.

• un micro is the common, everyday short form of un microphone.
• People almost always say micro in speech:
  • Allume ton micro. = Turn on your mic.
  • Coupe ton micro. = Mute your mic.

Micro is masculine, like microphone:

• un micro, le micro, mon micro.

Standard written negation in French uses ne … pas around the verb:

• fonctionne → ne fonctionne pas
  
  • Mon micro fonctionne.
  • Mon micro ne fonctionne pas.

In spoken French, people very often drop the “ne”:

• Mon micro ne fonctionne pas. (full, formal/standard)
• Mon micro fonctionne pas. (very common in conversation)

In writing (especially in anything formal or semi-formal), keep both parts: ne … pas.

Both word orders are correct:

1. Main clause first:

   • Je préfère écrire dans la messagerie quand mon micro ne fonctionne pas.

2. Quand-clause first:

   • Quand mon micro ne fonctionne pas, je préfère écrire dans la messagerie.

When the quand clause comes first, you normally add a comma before the main clause.
Meaning and grammar are the same; this is just a stylistic choice.

They’re very close in meaning, but:

• écrire dans la messagerie

  • Slightly more general/formal: “in the messaging system / inbox / chat.”
  • Could refer to different types of messaging (platform chat, internal messaging, etc.).

• écrire dans le chat

  • More colloquial and specific to chat windows (like Zoom/Discord chat).
  • Common in online/gaming/video-call contexts.

In many modern contexts (video meetings, online games), dans le chat may sound more natural in everyday speech, but dans la messagerie is perfectly correct and slightly more neutral.