Hi! Welcome to the Board!

I'm not quite sure what you mean by "Fandom". I know everyone else has been assuming you mean you want to write stories set in the PPC shared universe (interludes, missions, etc), but on the off chance you actually mean fandom as in "can I have permission to write fanfiction with OCs" (possibly a la OFU, where extreme badficcers have to graduate to go back to writing): That isn't something we even pretend to have any authority over IRL. While there are a lot of PPCers among OFU authors, that's all done in fun. The PPC IRL, the writing community whose members have been responding in this thread and others, has no authority over who writes fanfic or how they write it, and doesn't pretend to, either. So, if you're looking for permission to write fanfic including characters you've invented...congratulations! You don't need it. You never did. Depending on your age, you can even post it on multiple sites, if you want (there's often an age limit of thirteen, for legal reasons of some sort).

What we can offer is writing advice, both on and off the wiki. There have been multiple writing discussion threads on the Board (probably thousands or more over the years), and there's a dedicated writing channel on the Discord server that sees a lot of action. If you want to talk your ideas over with people, you've come to a good place.

And if I'm wrong, and you do mean "the PPC" when you say "Fandom", wonderful! See the previous replies, and good luck when you get to asking :)

~Z

As someone who has obtained Permission relatively recently, let me give you some tips.
The PPC is as much a community as it is a shared written universe. So if you wish to start creating PPC stories, you have to become a part of the community as well. You can start by making an introduction here on the Board and in the Discord chat, where you share a few things about yourself. Then you can hang out with the community in the virtual space for a bit, give us a chance to get to know you as a person. And once most of the community is familiar with you, you can start trying for Permission. If that seems like a long process, don't worry - there's more to the PPC than just the stories, and the gang here is genuinely welcoming and fun to be a part of. Plus, you don't have to wait forever - I got Permission after several months of being here.
In other words, have a little patience. :) And do read the Wiki articles for newbies, they explain the process much better and in more detail than I just did.

Here, see this PPC Wiki article on Permission. It's rather a formal process. The Wiki is also a great nexus to link to other PPC stories that you might like to read.