Following is a sample proxy service and fault handler sequence you can use as a starting point for handling faults when integrating with Reddit. Customize this sample to match your requirements.
Sample Proxy
<proxy xmlns="http://ws.apache.org/ns/synapse" name="reddit_sampleProxy" transports="https,http" statistics="disable" trace="disable" startOnLoad="true">
<target>
<inSequence onError="faultHandlerSeq">
<init>
</init>
<filter source="$axis2:HTTP_SC" regex="^[^2][0-9][0-9]">
<then>
<switch source="$axis2:HTTP_SC">
<case regex="401">
<!--Fill with your Error code value and expression-->
<property name="ERROR_CODE" value=""/>
<property name="ERROR_MESSAGE" value | expression />
</case>
<case regex="422">
<property name="ERROR_CODE" value=""/>
<property name="ERROR_MESSAGE" value | expression/>
</case>
<case regex="404">
<property name="ERROR_CODE" value=""/>
<property name="ERROR_MESSAGE" value | expression/>
</case>
<case regex="403">
<property name="ERROR_CODE" value=""/>
<property name="ERROR_MESSAGE" value | expression/>
</case>
<case regex="400">
<property name="ERROR_CODE" value=""/>
<property name="ERROR_MESSAGE" value | expression/>
</case>
<case regex="500">
<property name="ERROR_CODE" value=""/>
<property name="ERROR_MESSAGE" value | expression/>
</case>
<default>
<property name="ERROR_CODE" expression="$axis2:HTTP_SC"/>
<property name="ERROR_MESSAGE" value | expression/>
</default>
</switch>
<sequence key="faultHandlerSeq" />
</then>
</filter>
<respond />
</inSequence>
<outSequence>
<send></send>
</outSequence>
</target>
</proxy>