There is a flaw in the iPhone X Later App. When you go to post you are unable to click next on Instagram because of where the app information is in the top corner. This wasn't an issue until the X because of the screen going all the way into the corners. So the app is unusable with the iphone X. Need an update for this soon.
This is a flaw in the Instagram app. We have, however, implemented a work-around now which is live.
Update your Later mobile app if you don't see the workaround yet