User Import Bulk fail Bad Request

i already opened the file and read the content, i tried to run the import directly with Curl and it works fine. but with PHP, even i could open the file, read all content, get full path … i always get the same error.
this is my POSTFIELD:
-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"users\"; filename=\"$file\"\r\nContent-Type: text/json\r\n\r\n\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"connection_id\"\r\n\r\n**********\r\n-----011000010111000001101001\r\nContent-Disposition: form-data; name=\"external_id\"\r\n\r\n******\r\n-----011000010111000001101001--\r\n

on $file variable, i put the path, full path, content get stream, fopen, content…