To create a league you have to be logged in. Then go to the overview of the leagues, there you will find a button "Create a league".
After the league has been created, an initial export must be started from the Madden Companion App so that the league can be reached.
You need the Madden Companion App to export the data.
After logging into the app, select "Play Franchise" and then the league that you want to export.
Go to the export area there you will find an empty field in which you have to enter the API Url provided by Madden Leagues.
How do you find this url now?
After logging in to Madden-Leagues.com, select the league from your leagues that you want to export. In the Admin -> Settings area you will find the API Url. You have to enter this in the empty field in the Companion App and then select the week you want to export.
The data is transferred with a click on Export. It may take several minutes for the data to appear in Madden Leagues.