<?php...curl_setopt($ch,CURLOPT_SSL_CTX_FUNCTION,$someContextFunction);... Resulted in this output: PHP Fatal error: Uncaught Error: Undefined constant "CURLOPT_SSL_CTX_FUNCTION" in [snip] This constant is documented inhttps://curl.se/libcurl/c/CURLOPT_SSL_CTX_FUNCTION.html ...