The pro who answered your random DM with actual advice didn’t owe you a single word. Pay it forward when you’re the pro.

Nobody is obliged to help you. When somebody with real expertise answers a stranger’s question properly, they have taken time that was theirs and given it away with no prospect of return. That generosity is common enough to be taken for granted and rare enough to be worth counting. It is also entirely optional every single time.

Thank the person who did that for you, even if it was months ago, since they probably never heard whether it helped. Then answer the next message from someone a few steps behind you. You do not have to be an expert to be useful to them, only further along.