A recent Tumblr change added an extra layer of security, which broke XInbox. Luckily, I was preparing for this (starting with One-Click Postage, a couple of days ago), so XInbox is now updated to work with the changes.

If you can’t publish asks, go to XKit Control Panel > Other > Update All or wait for XKit to update itself, which might take someplace between 10 minutes to 1.5 hours, so Update All method is recommended.