So the page https://moodle.org/mod/data/view.php?id=7232 (having logged in) says...
"You need an account on moodle.org in order to post an advert. Login then click the "Add entry" tab. Adverts require approval before they are viewable by everyone. A pink background to your advert indicates that it is awaiting approval."
So clearly I have an account but the advice above needs updating as thats clearly not enough. I can see no "add entry tab"
Dom - have you previously posted Moodle jobs but not deleted them? When you click on moodle.org/jobs do you see the message underneath the bit you posted:
You may update your advert at any time by editing your entry. Please remember to delete your advert when the position is no longer available. You may post up to two adverts.