Where did I go wrong?

It's actually pretty standard. Which 4x holding is mp trying to represent. It looks more like 77 but he could easily have KT as well although it makes no sense for him to checkraise these hand. You represent AT+ and rarely something worse. Sometimes 88 99 but with JT QT KT he's behind against your bettingrange but he is unknown and he could possibly have 89 or some flushdraw. and consider it's lowstakes where people use to overplay toppair kind of hands, not really well considering the opponents range. Calldown is fine! Please don't post results when you post your next hand but i'm glad that you're willing to learn through handevaluations.

I would have 3-bet the flop. Top pair top kicker is pretty strong. A player who coldcalls preflop in the BB can have quite a few worse hands and we're 3 handed. When we're multi-way we need to be ahead a lot less often to make our 3-bet.

The turn and river look good though and you've played them well. The most likely hand MP represents is 77 and the occasional flush draw but after we just call on the flop he might think other value hands are ahead. Given that he didn't cap preflop we usually won't see MP holding an overpair so his worse value hands usually include other top pairs.

The river hits some flush draws, but the pot is very big. We beat worse Tx and club draws and he might only have a dozen combos of made hands.

We lose to 77, 44, KQ:heart:, KJ:heart, QJ:heart:, 98:heart: J8/J9:heart:... thats just 10 combos, and even if we toss in the occasional over pair we'll win often enough to call in such a large pot.

Its worth noting that when we have the A♥ it really cuts down on the number of ways he can improve on this river card.