I know the solution!!!
I was using a Mac, but it probably counts for other platforms as well.
When I compressed my resources into resources.zip, I was putting a folder called resources into the zip file itself.
The structure of the zip file came out like this:
resources.zip
resources
assets/
pack.mcmeta
pack.png
This is not what Minecraft expects.
Minecraft was looking for the following structure:
resources.zip
assets/
pack.mcmeta
pack.png
For example, in a Mac, instead of saying Compress "resources" into "resources.zip", I had to select all the items in resources and then click Compress # Items, change the zip file's name to resources.zip, and put it in the root of the map folder.
I hope that helped
