Can't produce to Confluent Kafka topic through Kafka REST API

I have a trouble producing to Kafka topic through Rest API proxy.

I have a running confluent kafka cluster in which I'd like to create a topic and produce a message to it using REST API.

For that purpose I have followed the documentation and created API key and secret.

I manage to create topic:

curl -X POST -H "Authorization: Basic <BASE64_ENCODED_AUTH_KEY_SECRET>"  \
-H "Content-Type: application/json" \
-d "{\"topic_name\":\"test1\",\"partitions_count\":6,\"configs\":[]}" \
https://pkc-xmzwx.europe-central2.gcp.confluent.cloud:443/kafka/v3/clusters/lkc-1zoqz/topics" | jq 

-------------------
returns:
{
  "kind": "KafkaTopic",
  "metadata": {
    "self": "https://pkc-xmzwx.europe-central2.gcp.confluent.cloud/kafka/v3/clusters/lkc-1zoqz/topics/test1",
    "resource_name": "crn:///kafka=lkc-1zoqz/topic=test1"
  },
  "cluster_id": "lkc-1zoqz",
  "topic_name": "test1",
  "is_internal": false,
  "replication_factor": 0,
  "partitions_count": 0,
  "partitions": {
    "related": "https://pkc-xmzwx.europe-central2.gcp.confluent.cloud/kafka/v3/clusters/lkc-1zoqz/topics/test1/partitions"
  },
  "configs": {
    "related": "https://pkc-xmzwx.europe-central2.gcp.confluent.cloud/kafka/v3/clusters/lkc-1zoqz/topics/test1/configs"
  },
  "partition_reassignments": {
    "related": "https://pkc-xmzwx.europe-central2.gcp.confluent.cloud/kafka/v3/clusters/lkc-1zoqz/topics/test1/partitions/-/reassignment"
  },
  "authorized_operations": []
}

MY PROBLEM: I can't produce to that topic (can't produce to ANY topic through Kafka Rest API) :

curl -X POST -H "Authorization: Basic <BASE64_ENCODED_AUTH_KEY_SECRET>"  \
-H "Content-Type: application/json" \
--data "{"records":[{"value":"S2Fma2E="}]}" \
"https://pkc-xmzwx.europe-central2.gcp.confluent.cloud:443/kafka/v3/clusters/lkc-1zoqz/topics/test1"  
    

-----------------
returns:
    {"error_code":405,"message":"HTTP 405 Method Not Allowed"}

ALSO TRIED LIKE THIS:

curl -X POST -H "Authorization: Basic <BASE64_ENCODED_AUTH_KEY_SECRET>"  \
                   -H "Content-Type: application/json" \
                    -d  "{ \"key\": {\"value\": \"S2Fma2E=\"} }" \
                   "https://pkc-xmzwx.europe-central2.gcp.confluent.cloud:443/kafka/v3/clusters/lkc-1zoqz/topics/test1/records"  

----------------
Returns the same:

    {"error_code":405,"message":"HTTP 405 Method Not Allowed"}

IDK if this has something to do with ACL management? Looking into that right now....

Are you using Confluent Platform (hosted) or Confluent Cloud API?

If the latter, this API is not supported, here's the documentation on what's supported by Cloud API: https://docs.confluent.io/cloud/current/api.html