"I have an appointment in April."

[KatBowman]

How strict is word order here? My translation 'randevum Nisan'da var' was wrong.

[Selcen_Ozturk]

that doesnt work, the word order in "var" sentences are sort of strict. You have to tell what is it that "exists" (randevum) always right before var.

[c6Rostyslav]

Is "nisanda bir randevum var" a correct translation? Is "bir" just unnecessary or shouldn't be used altogether?

[Lng52-._]

c6Rostyslav: That's my question as well.

[InesThomas2]

Why is Ben nisanda randevum var not correct?

[gogothegreat]

Because the word order is wrong and because you can't have the personal pronoun ben in the nominative case in sentences that are constructed with var. So, if you totally insist on using the (otherwise unnecessary) possessive pronoun here, the sentence should read like this:
Nisanda benim randevum var.