After baking the pavlova, let it cool and cut it in half. A moist liquid-like substance appears inside. (It does not leak out) Is this not ripe?
I baked it for 90 minutes at 120 degrees and cooled it in the oven for about 2 hours before cutting it.
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It sounds like your meringue is "weeping". This happens when the egg white proteins contract too much during cooking, squeezing liquid out.
Overcooking meringue leads to weeping. Using a small amount of starch in the meringue can help. So can pre-cooking the meringue by using hot sugar syrup (so-called "Italian meringue", which I think is unusual for a pavlova but I could be wrong).
Ultimately, though, it's really hard to reliably prevent weeping, and it does not indicate that the meringue is undercooked, unsafe, or un-delicious. Unless you can't stand to look at it, don't worry about it.