WSO2 Couldn't save JSON payload

Question

I use WSO2 EI 6.6.0 and Micro Integrator 4.0.0.
I have an api to get data, but for this I need to authenticate and get a token to use in a further request. for authentication I use separately created api and call it from first flow. For authentication I need to create a payload and send it in the request body to the server, but I get an error. The problem is repeated on different servers and I do not understand what is the reason.

My Auth API looks like this:

<api context="/auth" name="AuthGateway" xmlns="http://ws.apache.org/ns/synapse">
<resource methods="GET" uri-template="/gateway">
    <inSequence>
        <payloadFactory media-type="json">
            <format>{"username": "adm",  "password": "admin"}</format>
            <args/>
        </payloadFactory>
        <call>
            <endpoint>
                <http method="post" uri-template="https://1537-212-90-188-166.ngrok.io/auth/login">
                    <suspendOnFailure>
                        <initialDuration>-1</initialDuration>
                        <progressionFactor>-1</progressionFactor>
                        <maximumDuration>0</maximumDuration>
                    </suspendOnFailure>
                    <markForSuspension>
                        <retriesBeforeSuspension>0</retriesBeforeSuspension>
                    </markForSuspension>
                </http>
            </endpoint>
        </call>
        <log separator="&#xa;">
            <property expression="json-eval($)" name="log_auth"/>
        </log>
        <respond/>
    </inSequence>
    <outSequence/>
    <faultSequence/>
</resource>

My Data API looks like this:

<resource methods="GET" uri-template="/fieldCard?*">
  <inSequence>
     <propertyGroup>
        <property name="uri.var.version" expression="$url:version" scope="default" type="STRING"/>
        <property name="uri.var.size" expression="$url:size" scope="default" type="STRING"/>
        <property name="uri.var.page" expression="$url:page" scope="default" type="STRING"/>
     </propertyGroup>
     <log level="full" separator="&#xa;">
        <property name="version" expression="$ctx:uri.var.version"/>
        <property name="size" expression="$ctx:uri.var.size"/>
        <property name="page" expression="$ctx:uri.var.page"/>
     </log>
     <call>
        <endpoint>
           <http method="GET" uri-template="http://localhost:8290/auth/gateway"/>
        </endpoint>
     </call> .......

In the console I get messages:

[2022-05-02 19:16:12,962] ERROR {JsonStreamBuilder} - Error occurred while processing document for application/json java.lang.reflect.InvocationTargetException

Caused by: org.apache.axis2.AxisFault: #Can not parse stream. MessageID: urn:uuid:7ac6a4c9-0ed1-4973-87d4-69dad6d4a950. Error>>> #getNewJsonPayload. Could not save JSON payload. Invalid input stream found. Payload is not a JSON string. org.apache.synapse.commons.json.JsonStreamBuilder.processDocument(JsonStreamBuilder.java:43) ... 21 more

Caused by: org.apache.axis2.AxisFault: #getNewJsonPayload. Could not save JSON payload. Invalid input stream found. Payload is not a JSON string.

[2022-05-02 19:16:12,963] ERROR {DeferredMessageBuilder} - Error building message org.apache.axis2.AxisFault

[2022-05-02 19:16:12,964] ERROR {RelayUtils} - Error while building Passthrough stream org.apache.axis2.AxisFault

[2022-05-02 19:16:12,964] ERROR {SequenceMediator} - {api:AuthGateway} Error while building message. Error while building Passthrough stream org.apache.axis2.AxisFault: Error while building Passthrough stream

I removed the detailed stack trace. If it is needed to understand the problem - I can add it.
P.S. When calling the auth API directly I get the token and the response is correct.

[2022-05-02 19:20:17,560] INFO {org.apache.synapse.mediators.builtin.LogMediator} - To: http://www.w3.org/2005/08/addressing/anonymous
WSAction:
SOAPAction:
MessageID: urn:uuid:817185a7-39a4-4418-a696-72473672997d
Direction: request
log_auth = {"access_token":"eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX2lkIjoiMyIsInVzZXJfbmFtZSI6Im...
Payload: {"access_token":"eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VyX2lkIjoiMyIsInVzZXJfbmFtZSI6Im...

Please help me understand the problem.
UPD: I reinstalled the server because I thought the error might be there or I broke the config files. created a new project and wrote a new same thread, but the error still repeats.

Answer 1

Good. The problem was that Postman has a Header Accept-Encoding option. When this parameter was disabled, the request became correct and the response began to come without errors!