OpenAI ChatGPT (GPT-3.5) API error 400: "'user' is not of type 'object'"

I share with you my code bellow to get a response from a POST request with R from OPENAI chatgpt api :

param <- list(model = "gpt-3.5-turbo",
              messages = c("role" = "user", 
                           "content" = "Hello"))

result <- POST("https://api.openai.com/v1/chat/completions",
               body = param,
               add_headers(Authorization=openai_secret_key),
               encode = "json")

Here is the result :

>Response [https://api.openai.com/v1/chat/completions]
Date: 2023-03-02 16:28
Status: 400
Content-Type: application/json
Size: 158 B
{
“error”: {
“message”: “‘user’ is not of type ‘object’ - ‘messages.0’”,
“type”: “invalid_request_error”,
“param”: null,
“code”: null
}
}

So the user and the content part is not working but the model is working

Thanks a lot

In postman, I have this JSON working but can't make it work in R

{
   "model":"gpt-3.5-turbo",
   "messages":[
      {
         "role":"user",
         "content":"Hello!"
      }
   ]
}

If you run test.r the OpenAI API will return the following completion:

> [1] "\n\nHello! How may I assist you today?"

test.r

library(httr)
library(jsonlite)

OPENAI_API_KEY <- "sk-xxxxxxxxxxxxxxxxxxxx"

param <- list(model = "gpt-3.5-turbo",
              messages = list(list(role = "user", content = "Hello"))
         )
    
result <- POST("https://api.openai.com/v1/chat/completions",
               body = param,
               add_headers("Authorization" = paste("Bearer", OPENAI_API_KEY)),
               encode = "json")

response_content <- fromJSON(rawToChar(result$content))
print(response_content$choices[[1]]$content)