Why am I getting a 500 Response code from the SOAP API?
Oracle Service Cloud Connect Web Service for SOAP
The SOAP API returns a response code of 500 for failed authentication and the response body includes the faultcode wsse:FailedAuthentication and faultstring Access Denied. There are other reasons to receive a 500, and this can be checked by logging into the console with the username and password that are contained in the SOAP request. Checking the response body along with the response code will confirm whether invalid credentials are causing the request to fail.
For further information on the SOAP API, refer to Oracle Service Cloud Connect Web Services for SOAP.