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After reviewing this I suggest that we go with removing queryString altogether and just use url,

for an example, take GET request to "https://postman-echo.com/get?codes[web]=1&codes=2&test[]=2&codes=1"

it generates

library(httr)

url <- "https://postman-echo.com/get"

queryString <- list(
  `codes[web]` = "1",
  `codes` = "2,1",
  `test[]` = "2"
)

response <- VERB("GET", url, query = queryString, content_type(""))

content(response, "text")

which gives a response

{
  "args":{
    "codes":{
      "web":"1",
      "2,1":true
    },
    "test":["2"]
  }
. . .
}

But the actual response should be

"args": {
    "codes": {
      "0": "2",
      "1": "1",
      "web": "1"
    },
    "test": [
      "2"
    ]
  }
...

you can see this just by opening the above link

So the correct code generated should be

library(httr)

url <- "https://postman-echo.com/get?codes[web]=1&codes=2&test[]=2&codes=1"

response <- VERB("GET", url, content_type(""))

content(response, "text")

I have this change and can make it in the same pr if the maintainers believe that its appropriate.