Addon upload fails, no manifest found

I am updating an existing addon and I have a maven script that creates it so I expected it would go smoothly. I had problems like this in the past and they are usually answered by the need for the manifest file to be first. Zip doesn’t put it first, jar does, so back when I did it the first time I used jar. I am still using jar and I can see my manifest is first in the file, so this must be a different problem.
My addon consists of an actual jar file (contains the compiled code, plus source, docs, readme etc) all jar’ed up into the addon jar. Both jars have manifests which look to me to conform to the addon requirements (as they did last time). I downloaded my earlier addon to compare the two and the structure looks the same to me.
Any ideas?
Thanks for any help, I’ve attached the addon
28947.jar (1.17 MB)

I tested the version 3.1.0 Maven dependency from Directory and it is not working either. Directory thinks your top level jar is the actual artifact and adds it as a dependency. You should package it with zip instead of jar and follow the specification adding zip specific manifest attributes to point to the actual jar file inside your addon.

More details here:

Thanks for the quick reply. Turns out my file format was fine. I renamed it to .zip and it worked.