To use Mautic API calls, your application has to be authorized in Mautic instance you want to connect with. Mautic supports OAuth1 and OAuth2. Here we are focusing on OAuth2.
To create API credentials, go to your Mautic administration and follow these steps:
Step 1 -> Go to Mautic Configuration / API settings and set ‘API enabled’ to ‘Yes’. Save changes. 
Step 2 -> At the right side menu, the menu item ‘API credentials ‘ should appear. click on it.
Step 3 -> Create a new set of credentials.
Fill in the ‘Name’ (name of your app or something you recognize)
Redirect URI – Specify the URI that should be allowed API access ( For example, you need Mautic credentials to use it on testsite.com, then the Redirect URI will be testsite.com ). You can add a single or multiple websites separated with a comma.
For Convert Pro, you will need to add two URLs for a website:
http://testsite.com/wp-admin/admin.php?page=convertpro-mautic
http://testsite.com/wp-admin/
Make sure you select “OAuth2” as ‘Authorization Protocol’. Save new credentials
Mautic will generate ‘Public Key’ and ‘Secret Key’.
