This error code occurs while trying to signup with Match MY Email service if the user does not have API calls enabled. Thus the option “API Enabled” in the User’s profile within their Salesforce Organization is not checked.
To resolve this error the Salesforce Administrator must log into the Salesforce Organization and enable “API Enabled” for the user’s profile. To do so, go to Salesforce Setup and in left sidebar, under Administration Setup expand Manage Users and click on Profiles. Alternatively, you can click on Users to see what profile is actually assigned to the User having the issues.
Once presented with the profile name, click the name. In the example below, we are choosing the Standard User Custom profile.
As shown in the screenshot below, scroll down to the “Administrative Permissions” section. Check the box for “API Enabled” and save changes. The user should then be able to proceed with setting up their Salesforce Integration for Match My Email.