Misgendering
Referring to someone as a gender that isn't theirs.
Misgendering is using the wrong pronouns, honorifics or gendered words for someone. It runs from a slip mid-sentence to a deliberate refusal, and the two are not the same thing.
Accidental misgendering is survivable and common, especially early on. What determines how it lands is the response: a quick correction and moving on costs nothing, while an extended apology turns the moment into something the misgendered person now has to manage for you.
Sustained misgendering is different in kind. Repeated over months, it isn't a series of mistakes but a message, and it's one of the most reliable predictors of trans people leaving a workplace or a family.
The fix is unremarkable. Ask, use what you're told, correct yourself in three words, keep talking.