I can't login sandbox user on simulator

I created a new sandbox user for the pay test. I validated Email no problem so far. After that, I tried login on IOS(11) simulator(IPhoneX) but has an error:

"incorrect username or password"

I'm sure email and passwords correct.

How do I check my Apple login?

There is no "test users" for Sign In with Apple, yet. You need to use real accounts. Update: I had a call with an Apple engineer for during a WWDC 1-on-1 lab. They suggested a method to re-use the same account for Sign in with Apple.

How do I add a sandbox to my Iphone XR?

Sign In to the App Store with Your Sandbox Apple ID In iOS and iPadOS, the sandbox account appears in Settings > App Store after the first time you use the device to attempt a purchase in a development-signed app. There's no need to sign out of the non-Sandbox Apple ID. Sign in using a Sandbox Apple ID.

Just solved this by logging in with my new sandbox user at icloud.com and agreeing to their T&Cs. Simulator login then works a charm!