Constant contact API key instructions not working

Hi there. I’m trying to follow these instructions to connect Constant Contact:

1. Login to the Constant Contact V3 Portal and create a “New Application”.
2. Enter “MailOptin” as the application name and click “Save”.
3. Copy your Constant Contact API Key and paste it into the API Key field below.
4. Click the “Generate Secret” button, go through the secret generation process and paste the resulted key in the “App Secret” field below.
5. Paste the URL https://example.com/wp-admin/admin.php?page=mailoptin-integrations&moauth=ctctv3 into the Redirect URI field and click “Save” in the top right corner of the screen.
6. After saving, click the Authorize button that will appear to connect your account. Learn more

However, Constant Contact is now asking additional questions about “Implicit Flow,” “PKCE,” “Refresh Token,” etc. Can you provide more information on what I need to select? Thanks!