Occasionally get "attempt to apply non-function" error when applying getForm

I'm using getForm to repeatedly pull data from an api. Sometimes the program finishes, and other times after some amount of iterations, I get the following error message: ``` Error in curlPerform(url = url, curl = curl, .opts = .opts) : attempt to apply non-function In addition: There were more than 50 warnings (use warnings() to see the first 50) > traceback() 5: .Call("R_curl_easy_perform", curl, .opts, isProtected, .encoding, PACKAGE = "RCurl") 4: curlPerform(url = url, curl = curl, .opts = .opts) 3: getURLContent(uri, .opts = .opts, .encoding = .encoding, binary = binary, curl = curl) 2: getForm("https://xx", .params = parval) 1: fromJSON(getForm("https://xx", .params = parval)) at #32 ``` the warnings are: ``` In RCurlIconv(str, from = "C99", to = encoding) : UTF-8 not supported iconv entries ``` Thanks for your help!