wso2 issues using call mediator on magento2 api - wso2

Question

I'm trying to create a service chain using a wso2 sequence with a payload factory and call mediator.
I'm using wso2 3.2.0 and Magento 2.4.1.
My goal is to ask Magento a token using admin credentials, and returning the token to the client. The payload to make the request should be defined inside the sequence, and there should also be other call mediators after the first one.
I've defined my API with the following definition, and I'm using dynamic endpoints
openapi: 3.0.1
info:
title: Magento
version: v1
servers:
- url: /
security:
- default: []
paths:
/call:
get:
parameters: []
responses:
'200':
description: ok
security:
- default: []
x-auth-type: None
x-throttling-tier: Unlimited
x-wso2-application-security:
security-types:
- oauth2
optional: false
post:
parameters: []
responses:
'200':
description: ok
security:
- default: []
x-auth-type: None
x-throttling-tier: Unlimited
x-wso2-application-security:
security-types:
- oauth2
optional: false
components:
securitySchemes:
default:
type: oauth2
flows:
implicit:
authorizationUrl: 'https://test.com'
scopes: {}
x-wso2-cors:
corsConfigurationEnabled: false
accessControlAllowOrigins:
- '*'
accessControlAllowCredentials: false
accessControlAllowHeaders:
- authorization
- Access-Control-Allow-Origin
- Content-Type
- SOAPAction
- apikey
- testKey
accessControlAllowMethods:
- GET
- PUT
- POST
- DELETE
- PATCH
- OPTIONS
x-wso2-production-endpoints:
type: default
x-wso2-sandbox-endpoints:
type: default
x-wso2-basePath: /magento/v1
x-wso2-transports:
- http
- https
x-wso2-response-cache:
enabled: false
cacheTimeoutInSeconds: 300
The sequence for my API looks like so,
<?xml version="1.0" encoding="UTF-8"?>
<sequence name="service_chain_request_magento" trace="disable" xmlns="http://ws.apache.org/ns/synapse">
<property action="remove" name="REST_URL_POSTFIX" scope="axis2"/>
<property name="FORCE_HTTP_1.0" scope="axis2" type="STRING" value="true"/>
<property name="DISABLE_CHUNKING" scope="axis2" type="STRING" value="true"/>
<payloadFactory media-type="json">
<format>{"username":"<username>","password":"<pwd>"}</format>
<args/>
</payloadFactory>
<property name="messageType" value="application/json" scope="axis2"/>
<call blocking="true">
<endpoint>
<http method="post" uri-template="http://<magento_ip>/index.php/rest/all/V1/integration/admin/token">
<timeout>
<duration>6000</duration>
<responseAction>fault</responseAction>
</timeout>
</http>
</endpoint>
</call>
<enrich>
<source type="body" clone="true"/>
<target type="property" action="child" property="body_of_first_call"/>
</enrich>
<log level="full"/>
</sequence>
Where everything inside <> is, of course, replaced with proper values.
When I try to call my API POST - https://<ip>:8243/magento/v1/call using this sequence, I get the following result:
{
"message": "One or more input exceptions have occurred.",
"errors": [
{
"message": "\"%fieldName\" is required. Enter and try again.",
"parameters": {
"fieldName": "username"
}
},
{
"message": "\"%fieldName\" is required. Enter and try again.",
"parameters": {
"fieldName": "password"
}
}
],
}
even though, inspecting the logs, this is the response:
INFO - LogMediator {api:admin--Magento:vv1} To: http://<magento_ip>/index.php/rest/all/V1/integration/admin/token, MessageID: c6b5eb10-89a1-42df-9f0d-098d605dae91, correlation_id: c6b5eb10-89a1-42df-9f0d-098d605dae91, Direction: request, Payload: "brni5ub8o4vfltfups9swrwk3biw3cd4"
As what I can understand, the Payload field is correctly returning the expected response from Magento rest APIs, but it looks like the REST client I'm using (both Postman and the wso2 console) are returning the error response from the API, like the request is made a second time without the post body.
If I replace the call mediator with the To header like this:
<header name="To" scope="default" value="http://<magento_ip>/index.php/rest/all/V1/integration/admin/token"/>
the call just works and returns the expected payload, but then I cannot chain other call mediators.
Here's the specs about the Magento API I'm calling https://magento.redoc.ly/2.4.2-admin/tag/integrationadmintoken
How can I resolve this?
Thanks in advance