Can not pass parameters to REST API WSO2 in JSON format - wso2

Question

Does anyone know about this error?
I'm passing json to the request like:
{"param1":"hello world"}
Property Mediator
action:set,
set action as: expression,
type: string,
expression: json-eval($.param1),
scope: axis2
Seems like API cannot extract the "hello world" value, because logs show:
param1=null
Works perfectly with value:
<property name="param1" value="HELLO WORLD" scope="default" type="STRING"/>
Null this way:
<property name="param1" expression="json-eval($.param1)" scope="axis2" type="STRING"/>
API Source View:
<api xmlns="http://ws.apache.org/ns/synapse" name="REST" context="/api/post">
<resource methods="POST" url-mapping="/createInvoice">
<inSequence>
<property name="operation" value="createInvoice" scope="default" type="STRING"/>
<log level="full" separator="|">
<property name="operation" expression="get-property('operation')"/>
<property name="step" value="request"/>
</log>
<property name="param1" expression="json-eval($.param1)" scope="axis2" type="STRING"/>
<property name="param2" expression="json-eval($.param2)" scope="default" type="STRING"/>
<log level="full" separator="|">
<property name="param1" expression="get-property('Axis2','param1')"/>
<property name="param2" expression="$ctx:param2"/>
</log>
<dbreport>
<connection>
<pool>
<dsName>OEBS_DS_MOS</dsName>
</pool>
</connection>
<statement>
<sql>call procedure.create_invoice(?,?)</sql>
<parameter expression="get-property('Axis2','param1')" type="VARCHAR"/>
<parameter expression="$ctx:param2" type="VARCHAR"/>
</statement>
</dbreport>
<payloadFactory media-type="json">
<format>{"response" : {"code" : "00", "message" : "success"}}</format>
<args/>
</payloadFactory>
<property name="RESPONSE" value="true" scope="default" type="STRING"/>
<property name="messageType" value="application/json" scope="axis2" type="STRING"/>
<property name="contentType" value="application/json" scope="axis2" type="STRING"/>
<respond/>
</inSequence>
<outSequence>
<payloadFactory media-type="json">
<format>{"response" : {"code" : "02", "message" : "outSeq"}}</format>
<args/>
</payloadFactory>
</outSequence>
<faultSequence>
<payloadFactory media-type="json">
<format>{"response" : {"code" : "01", "message" : "fail"}}</format>
<args/>
</payloadFactory>
</faultSequence>
</resource>
</api>

Answer 1

The problem is with scope of your property.
You set value from JSON to property in scope="axis2", so you can read that property using: get-property('axis2', 'param1'), or $axis2:param1.
Or you can set property in default scope, and now you can use: get-property('param1'), or $ctx:param1.
This documentation explains it exactly.