I am using the latest Mac OS update (Mojave) and the latest version of Xcode (10.0), and I'm just trying to update an app.
When I try to log into Application Loader it says "To use this application, you must first sign in to iTunes Connect and sign the relevant contracts"
Things I've tried:
1. Some of the forums said if you try accessing Application Loader through Xcode it will prompt you to agree to something and then will work. This did not prompt me for anything and didn't work for me though it seemed to do the trick for many people.
2. I contacted apple support and they told me that there was a pending request on my iTunes account for a paid app contract that needed to be filled out. (This didn't make any sense because we don't have any paid apps, but they said the request couldn't be retracted.) So I filled this out and it processed successfully, but I still got the same message. I tried every day for three days just to make sure.
3. Apple support then told me to make sure I had everything updated (OS as well as Xcode) which I did, still no luck.
Apple support has now said they've passed me on to their "engineering" team, but I haven't gotten a response from them for 2 days even after sending follow-up emails. If anyone has any suggestions I'd be very happy to hear them.
Responding to my own post because I finally got it to work!
What I did to fix it was completely uninstalled Xcode and reinstalled the latest version 10. I think the reason this worked is because it made me reaccept all the terms and agreements. I then got to Application Loader by opening it through Xcode and was able to log in and do everything I needed.
You also have to make sure that your iTunes account that you're installing Xcode with has a bank account and phone number associated with it. (Apple support got back to me and had that piece of advice. Recording it here in case it's an issue for anyone else.)