I've done a fair amount of searching and can't find a straight answer anywhere.
The free tiers on most of what I've tried are basically useless — you get just enough to see that real people are there, then hit a wall the second you try to actually message anyone.
Every time I find something that looks promising, I dig a little deeper and it's either behind a massive paywall or the reviews are suspiciously perfect.
Feel free to share whatever has worked for you, even if it's not the obvious answer.