UPDATE:
It worked once I removed all the chinese characters in mod description, so I guess the system is racist Kappa
So I published a custom scenario through the in-game system and shared it to my friends, they told me that for some reason they just coudlnt subscribe to it. So I tried to subscribe to my own mod and also failed.
I then tried to zip it and publish through the aoe website, still no luck. Turned out the folder with the mod title did came to my subscribed mod directory, yet the folder contained nothing other than the json file.
I managed to publish other random stuff (eg. rms / cs / ui mod) afterwards, so any chance theres something wrong with my custom scenario?
PS. Files and folders are all in english, mod description and triggers in the scenario contain Chinese characters tho.