I'm having no problem setting them. They appear when doing /lp user meta info. But when trying to show the values in places like actionbar, chat, tab, etc, by using the placeholder "%luckperms_meta_%".

It doesn't give errors or anything. It simply keeps showing as a blank space there.

It used to work before, and my procedure was the same.

I'm on Spigot 1.12 and java 1.8.
I have the last version of the Luckperms, PlaceholderAPI and MvdwPlaceholders.
I have also already downloaded the extension through the commands /papi ecloud...

I'm using the last version of the expansion: https://imgur.com/a/a0U5L

I also have LuckPermsMVdWHook.jar installed correctly.

I got what the isse was. I was setting the meta key with the first letter as capital, while on the placeholder I wrote in on lower case. Now it works.