Does the prayer become void if the muezzin says in the call to prayer "Ashhadu la ilaha illallah" (I bear witness that there is no god but Allah) instead of "Ashhadu an la ilaha illallah" (I bear witness that there is no god but Allah)?

The melodic intonation (laḥn) of the muezzin in the adhan is disliked (makrooh) if it does not alter the meaning. However, if it alters the meaning, it is forbidden (haram) and invalidates the adhan. If the melodic error (laḥn) changes the meaning, the adhan is not considered valid, but the prayer (salat) remains valid in all cases.