Click on New Integration button on the top right side of the page.
Select Access an API radio box.
Select Adobe Analytics under Experience Cloud and then select OAuth Integration from the list below.
A new page comes up which asks for the integration details. In this page
Enter an Integration Name and Description. Give your integrations accurate and descriptive names. Integrations are shared with developers within your organization, so choose a name that is clear and easily understood.
Specify the platform for your new integration (Web, Android, or iOS).
Specify the Default Redirect URI and Redirect URI Patterns. This tells Adobe where to direct your end users during or after the Adobe ID login process.
Prove that you are not a robot.
Click Create integration.
When creation is confirmed, visit the Overview page for your new integrations that contain the newly generated credentials
Overview page gives you two set of IDs - Client ID (API Key) and Client Secret, you would need this to generate an access token.