login failure

I am still working on iris-for-money app: https://github.com/oliverwilms/iris-for-money

Account.csp posts a rest call with _SYSTEM username and the password.

xhttp.open("POST", "/restapi/sql/" + query, true,"_SYSTEM","SYS");
xhttp.send();

/restapi web application has Password Authentication Method enabled.

SYS is the correct password for _SYSTEM user.

I do not understand why I see login failure in Audit database.