How to delete data on a server via an API and DELETE request in httr

I'm new to this whole API thing and certainly don't understand the full logic, but hope you can help me out here.

Please note that I can only provide a generic example without a reproducible example since the site I want to access requires a paid login.

What I want to do is to delete certain values from a data column on the server.

The data on the server is a survey with each column representing a survey question. I now want to delete from the column "xyz" the case with a value of "abc".

The help page from said website provides the following help on how to delete data:

http://release.decipherinc.com/s/local/beacon.html#data-input-and-output-modify-data-delete

And this is how I tried to achieve deleting the data:

library(httr)
library(tidyverse)
library(jsonlite)

my_data <- data.frame(xyz = c("abc", "def", "ghi"))
todelete <- my_data %>%
  filter(xyz == "abc")

my_platform_key <- "testkey"

# small function for the URL request
api_delete <- function(path)
{
  url <- paste0("release.decipherinc.com/api/v1/", path)
  add_headers(my_platform_key)
  DELETE(url, add_headers('x-apikey' = my_platform_key))
}

delete_request <- api_delete("surveys/MYSURVEY/data/edit?mode=delete&key=xyz&data=todelete")

I guess the problem might be with how I specify the data parameter. The help page says it needs to be an array, but not sure if simply passing a data frame is sufficient.

When I run this code followed up by: content(delete_request, encoding = "UTF-8") the response code is 400, so indicating that it didn't work (obviously):

data: expected an array, not string

What do I need to change in my code so that it will work?

Update

Digging deeper into the topic I found some additional information, but it still doesn't work. According to some other SO post, I tried the following:

library(jsonlite)
library(httr)
args <- list(key = unbox("xyz"),
             data = todelete,
             mode = unbox("delete"))

body <- toJSON(args)

DELETE(url         = "release.decipherinc.com/api/v1/surveys/MYSURVEY/data/edit",
       add_headers('x-apikey' = my_platform_key),
       body = body,
       encode = "json")

I checked the content of body and it looks exactly how it is described in the linked documentation, but it still doesn't work:

{"key":"xyz","data":[{"xyz":"abc"}],"mode":"delete"}

And the server response is:

Response [...URL...]
  Date: 2020-04-04 17:50
  Status: 400
  Content-Type: application/json
  Size: 72 B
{
 "$error": "missing argument 'data'",
 "$code": 400,
 "extra": null
}

Solution

OK, I figured it out on my own with a lot of trial and error. I was missing one particular parameter in my function, i.e. content_type. The code below works:

library(httr)
library(tidyverse)
library(jsonlite)

my_data <- data.frame(xyz = c("abc", "def", "ghi"))

todelete <- my_data %>%
  filter(xyz == "abc")

my_platform_key <- "testkey"

args <- list(key = unbox("xyz"),
             data = todelete,
             mode = unbox("delete"))

body <- toJSON(args)

DELETE(url         = "release.decipherinc.com/api/v1/surveys/MYSURVEY/data/edit",
       add_headers('x-apikey' = my_platform_key),
       content_type("application/json"),
       body = body,
       encode = "json")