I send a soap message into http://localhost/api/soap/mantisconnect.php
<soapenv:Envelope xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:man="http://futureware.biz/mantisconnect">
<soapenv:Header/>
<soapenv:Body>
<man:mc_projects_get_user_accessible soapenv:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/">
<username xsi:type="xsd:string">user</username>
<password xsi:type="xsd:string">psswd</password>
</man:mc_projects_get_user_accessible>
</soapenv:Body>
</soapenv:Envelope>

and getting answer

<SOAP-ENV:Envelope SOAP-ENV:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:SOAP-ENC="http://schemas.xmlsoap.org/soap/encoding/">
<SOAP-ENV:Body>
<SOAP-ENV:Fault>
<faultcode xsi:type="xsd:string">Server</faultcode>
<faultactor xsi:type="xsd:string"/>
<faultstring xsi:type="xsd:string">Error Type: SYSTEM NOTICE,
Error Description: Array to string conversion</faultstring>
<detail xsi:type="xsd:string"/>
</SOAP-ENV:Fault>
</SOAP-ENV:Body>
</SOAP-ENV:Envelope>