remote: Permission to haiku/haiku.git denied to maverickcodex18.
fatal: unable to access ‘GitHub - haiku/haiku: The Haiku operating system. (Pull requests will be ignored; patches may be sent to https://review.haiku-os.org).’: The requested URL returned error: 403
Seems you’re trying to push your changes to the Github mirror of Haiku’s source repo.
I suggest reading (and following) the Get the Haiku Source Code / Pushing Patches to Haiku 101, but…
As you already have a clone in your machine, you might only need to change the “git remotes”, so it points to some repo you have permissions to push (eg, your personal fork of Haiku over Github), or to Haiku’s Gerrit (but you need to properly setup your accont there before being able to push… making sure your email address match the one on your git config, and either setting a https password, or uploading your ssh public keys).
Just so you have a point of reference on how to change/add git remotes… From the linked guide above:
To submit a patch, you can change the remote URL of the Haiku repository to Gerrit using this command:
git remote set-url origin ssh://$USER@git.haiku-os.org/haiku
Hope it helps a little.
Also, @robicodex18, if you’re working on https://dev.haiku-os.org/ticket/16719, be aware of an existent previous patch implementation, and the review comments there. Might prove helpful.