Inbound SOAP API call gives 302 response code. 

The resource path is incorrect. Request to the instance comes in like this:
uri=/table_name.do?SOAPchange.do?SOAP&displayvalue=all

System will process it as a SOAP request only when SOAP query parameter is sent. However, the 2 query parameters sent are:
SOAPchange.do?SOAP=
displayvalue=all

This is why this request is treated as a UI transaction and is redirected to the SSO login page which is the 302

Make sure the end point is in the correct format. It should be /table_name.do?SOAP&displayvalue=all