OK, so the Failed Login was my test call on your Application settings in Auth0 Server. You can ignore it.
Right now you have Application Type Credential settings that are breaking your token flow. From another thread:
And you’ve also helped us find a UI bug that might confuse the issue further. Here’s how to turn these off in order to restore… uh… order.
First, in your Application ➔ Settings in Manage, if you do NOT have the Credentials tab visible, then scroll to the Application Type and change it to Regular Web Application. The following Note: dialog will appear beneath . You can click View Credentials there OR scroll up and the Credentials tab will now be visible.
Ok.
Second, in the Credentials settings there, you’ll find your Authentication Methods is set to Client Secret (Post). Change this by setting it back to the default of None.
Lastly, you can return to Application ➔ Settings tab and return the Application Type back to Native, and you should be good to go.
LMK how you get on. We’ll address the settings bug that allows Credentials changes like Client Secret (Post) to accidentially remain hidden and on in the background.