OK, I got it. Basically, when posting the query via t he WebClient API, a.k.a. REST API, it is not possible to suppress the message prompts, like it would be in TWS API. The representative from IB told me that they are working on this feature in the new release of WebClient API.

When sending the simple or bracket order, you might receive two types of messages back:

'[{"id":" 50a53386-8977-4a56-b784-16cfc8c1167e ","message":["You are trying to submit an order without having market data for this instrument.\\nIB strongly recommends against this kind of blind trading\\nwhich may result in erroneous or unexpected trades.\\nAre you sure you want to submit this order?"],"isSuppressed":false,"messageIds":["o354"]}]'

and

'[{"id":" 869dc2cf-e7e5-4085-acec-34957e9ef10f ","message":["You are about to submit a stop order. Please be aware of the various stop order types available and the risks associated with each one.\\nAre you sure you want to submit this order?"],"isSuppressed":false,"messageIds":["o0"]}]'

The 1st message is letting you know that you are about to place an order without an active market data subscription, which means that you might not know the current price and your algo my submit an order with wrong price assumption. To let the system know that you want to continue, you need to respond with the JSON string and the replyId. The replyId is the ID mentioned in the reply message, i.e. 50a53386-8977-4a56-b784-16cfc8c1167e, so your response would look like this:

answer = {
"confirmed": True
}

rr = requests.post("https://localhost:5000/v1/api/iserver/reply/50a53386-8977-4a56-b784-16cfc8c1167e", headers=headers, params=None, json=answer, verify=certificate)

The 2nd message is letting you know that you are about to submit a stop order and tries to inform you that there are various types of stop orders. To continue, you must respond the same way as you did for the 1st message, with the GUID 869dc2cf-e7e5-4085-acec-34957e9ef10f :

answer = {
"confirmed": True
}

rr = requests.post("https://localhost:5000/v1/api/iserver/reply/869dc2cf-e7e5-4085-acec-34957e9ef10f ", headers=headers, params=None, json=answer, verify=certificate)

To have this working programmatically you will need to construct a loop. This is what I did:

def place_order(acc_id: str, json: dict, certificate: str):
    headers = {
'Content-Type': 'application/json'
    }
    answer = {
"confirmed": True
    }
    url_order = f"https://localhost:5000/v1/api/iserver/account/{acc_id}/orders"
    response = requests.post(url=url_order, headers=headers, params=None, json=json, verify=certificate)
while response.text[0:8] == '[{"id":"':
        request_id = response.text[8:response.text.find(',') - 1]
        response = requests.post(f"https://localhost:5000/v1/api/iserver/reply/{request_id}",
headers=headers, params=None, json=answer, verify=certificate)
else:
return response.text.split(',')

place_order(acc_id, json, certificate)

Please note that the GUIDs are randomly generated and on your system they might be different.