Is/Can Aponia be part of Eudaimonia?
Definitely!
In two places, the supreme pleasure of the gods is referred to as παντελῆ εὐδαιμονίαν (pantelē eúdaimonían) "complete happiness" (Laértios 10.116) and τελείαν εὐδαιμονίαν (teleían eùdaimonían) “perfect happiness” (On Piety 13), so there are equivalencies between "happiness", "pleasure", and "blessedness". "Complete happiness" (as of the gods) does require painlessness (aponía).
In the Epistle to Menoikeús, Epíkouros also writes that "those necessary [desires] are [instrumental] to happiness" (10.127), being the reduction of hunger, thirst, and cold.
In my view Epicurus reached Eudaimonia the happy life but he had extreme pain, so no aponia, or do I miss something ?
I agree. I think his reconstructed sayings, and his Last Will document that he was at least, generally happy when he died. "Even if the wise were tortured on a rack, they would be happy" (Laértios 10.118). It was inevitable, and, like Metródōros, he accepted it as any other natural event.
He was definitely "happy" in the general sense of neither grieving nor complaining, and he "expired undauntedly" (On Death 39.15), but I wouldn't say that he was enjoying "perfect happiness" or "pure pleasure" just because his mind was untroubled. Ataraxia is just half the formula.