Single Sign-On user_id cannot be null

[qualia]

I'm attempting to utilise single sign on in WHMCS, but get a PDO error "Uncaught exception 'PDOException' with message 'SQLSTATE[23000]: Integrity constraint violation: 1048 Column 'user_id' cannot be null' in /whmcs/vendor/illuminate/database/Connection.php:444". I have the correct request parameters as described here: http://docs.whmcs.com/API:CreateOAuthCredential. The params I'm using are:

 

username:xxxxxxxx

password:xxxxxxxxx

action:CreateOAuthCredential

grantType:single_sign_on

scope:clientarea:sso clientarea:profile

description:Test SSO

serviceId:<USER ID HERE>

responsetype:json

 

I put some logging in Connection.php and it appears WHMCS is attempting to insert into `tbloauthserver_clients`, but there is no user_id. How do I pass user_id as a parameter? What am I doing wrong?