Offer inbound SOAP API Call for anonymous visitors

Hi, 

I have an use case to pop up birthday offers using offer interaction module in mobile App channel. For this I have prepared the soap call for identified users and its working fine by returning the response with proposition id and HTML representation. But i cant use the same SOAP call for anonymous visitors even though my offer space is linked with fall back mechanism to retrieve offers from visitors offer space . Let me know if anyone of you have come across this use case. 

<SOAP-ENV:Envelope xmlns:SOAP-ENV='http://schemas.xmlsoap.org/soap/envelope/'>

                <SOAP-ENV:Body>

                                           <Propose>                                            

                                                <targetId>4567</targetId>

                                                <maxCount>10</maxCount>

                                                <context></context>

                                                <!--optional-->

                                                <categories></categories>

                                                <!--optional-->

                                                <themes></themes>

                                </Propose>

                </SOAP-ENV:Body>

</SOAP-ENV:Envelope>

Thanks,

Moseen