Advice Needed After Accidental Consumption

As-salamu alaykum everyone. I come from a Shi'a family and am still underage. My mother is quite devout, while my father is more relaxed in his practice. Honestly, some extended family on my father's side don't follow Islam closely, but I focus on my own path. My father occasionally consumes alcohol and is open about it. Lately, as he prepares for a trip abroad, he's been taking me and my younger sister out to eat to spend time together. Yesterday, he took me to a restaurant and kept offering me some of the beer he was drinking, even ready to order me my own. I'll be honest, before we went, I had joked about trying it, and he took that seriously. After he asked multiple times, I firmly said no, affirming my love for Allah and my deen. Today, we went to another place with my sister. Things were fine until the waiter came, and my father ordered a beer. He offered it to both of us; we refused, but he persisted. I looked at the bottle and saw '100% malt.' I remembered a non-alcoholic malt drink called Laziza that we used to have, so I thought this was similar. I quickly searched on my phone if malt was alcoholic, and an answer said no-I should have looked deeper. I took a small sip and immediately tasted how bitter and strong it was; it clearly contained alcohol. My sister was about to try it, but I stopped her. I checked again and realized Laziza is non-fermented, while this drink was not. I felt terrible and told my father, who said it was okay since he allowed it. I've also read that prayer isn't accepted for 40 days after such an act, and sincere repentance is needed. Honestly, I don't know exactly how to repent for this, as I haven't intentionally done anything haram before. The drink was Carabao Lager. I didn't feel any physical effects, so maybe the sip was too small to matter? I'm feeling very guilty and would appreciate any advice or clarification on how serious this is. Jazakum Allahu khayran.