You need to provide the XML configuration of the event receiver. I tried the following with SOAP UI and it works.
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:adm="http://admin.receiver.event.carbon.wso2.org">
<soapenv:Header/>
<soapenv:Body>
<adm:deployEventReceiverConfiguration>
<!--Optional:-->
<adm:eventReceiverConfigXml><![CDATA[<eventReceiver xmlns="http://wso2.org/carbon/eventreceiver" name="httpReceiver" statistics="disable" trace="disable">
<from eventAdapterType="http">
<property name="transports">all</property>
</from>
<mapping customMapping="disable" type="json" />
<to streamName="org.wso2.event.sensor.stream" version="1.0.0" />
</eventReceiver>]]>
In a multi tenant environment, use the respective tenant admin's credentials for basic authentication. Then it will deploy the event receiver in the correct tenant. When deploying DAS will print a log as follows,
[2016-02-11 17:40:39,670] admin@test.com [1] [DAS] INFO {org.wso2.carbon.core.services.util.CarbonAuthenticationUtil} - 'admin@test.com [1]' logged in at [2016-02-11 17:40:39,670-0700]
[2016-02-11 17:40:39,674] admin@test.com [1] [DAS] INFO {org.wso2.carbon.event.receiver.core.internal.util.helper.EventReceiverConfigurationFileSystemInvoker} - Event receiver configuration saved to the filesystem :httpReceiver.xml
[2016-02-11 17:40:39,675] admin@test.com [1] [DAS] INFO {org.wso2.carbon.event.input.adapter.core.internal.InputAdapterRuntime} - Connecting receiver httpReceiver
[2016-02-11 17:40:39,676] admin@test.com [1] [DAS] INFO {org.wso2.carbon.event.stream.core.internal.EventJunction} - Producer added to the junction. Stream:BAM_MESSAGE_TRACE:1.0.0
[2016-02-11 17:40:39,676] admin@test.com [1] [DAS] INFO {org.wso2.carbon.event.receiver.core.EventReceiverDeployer} - Event Receiver configuration successfully deployed and in active state: httpReceiver