Since the SRRecurringAPI is a server servlet, authorization is required using valid API admin login credentials.
First, make sure you are using a valid API admin. If you aren’t using valid API admin credentials, see BB744888 to learn how to create an API admin.

If you are using a valid API admin and it still isn’t working, you need to modify the permissions being granted. To do this:
1.       Login to your admin panel
2.       Go to Constituent360 > Groups
3.       Click the “Administrator Group List” tab
4.       Find the group called “API Administrators” and click “Edit Permissions” under the actions tab
5.       Next to “What type of permissions do you want to edit?” click the dropdown list and select “Recurring Gifts”, then click “Choose”
6.       Change the Default Permission to “Recurring API”
7.       Click Save
8.       You should now see a notice at the top of the page that says “The permissions for this group have been saved successfully”

The SRRecurringAPI servlet should now work without displaying an error code 3.