What is the format of the body of a post request multipart/form-data

Hi There! I want to send data (2 texts datas and a file) with post request to a rest API with multipart/form-data.
I thought I had to completely rewrite the entire request body, and I did it (I made a program for create it automatically).
I know that the body of my http request is good, however in this context I don’t know what format I should use.
Here my AT commands:

AT+QHTTPCFG="contextid",1
AT+QHTTPCFG="requestheader",1
AT+QHTTPCFG="responseheader",0
AT+QHTTPCFG="contenttype",3

//Set the URL which will be accessed
AT+QHTTPURL=132,80 
http://bigfelfelrandomsite/api/?user=user&function=upload_file&ref=14&sign=123456thtake5ou4n1es
OK (NICE!)

AT+QHTTPPOST=647,80,80
--Content-Type: multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW

----WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="key"

12345678910111213141516171819021222324252627
----WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="resource_type"

1
----WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="collection_add"

20
----WebKitFormBoundary7MA4YWxkTrZu0gW
Content-Disposition: form-data; name="userfile"; filename="data_random_0.txt"
Content-Type: text/plain

i don't like http
----WebKitFormBoundary7MA4YWxkTrZu0gW--


OK (Oh great!!)
+CME ERROR(402)(Ah...) ==> delay time

AT+QHTTPREAD=80 

(error)

Please help me!!
Thank You!

hello ,could you please tell us your current firmware version, so that we can loop dedicated moderator to support this issue, thanks~