How to encode foreign characters for importing to shopify via API using PHP and CURL – Magento

Im trying to import our customers from our Magento site to Shopify via the API. Im using PHP and CURL

My script works fine for most of our customers but its having trouble with any names that have foreign characters in, I get the question mark symbol when echoing the variables with the foreign characters in and the API call just fails and no customer is created.

Strangely if I copy the JSON object into Insomnia and run the API call it works fine even with the foreign characters so Im assuming Insomnia is adding some encoding that my script isnt.

Im assuming I have an issue with character set but not sure what I need to change it to or if I’ve set it wrong.

Heres my Curl code:

                $curl = curl_init();
                curl_setopt($curl, CURLOPT_URL, $url);
                curl_setopt($curl, CURLOPT_HTTPHEADER, array('Content-Type: application/json'));
                curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
                curl_setopt($curl, CURLOPT_VERBOSE, 0);
                curl_setopt($curl, CURLOPT_HEADER, 1);
                curl_setopt($curl, CURLOPT_CUSTOMREQUEST, "POST");
                curl_setopt($curl, CURLOPT_POSTFIELDS, $json_string);
                curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
                $response = curl_exec ($curl);
                curl_close ($curl);

and Ive also tried declaring it as UTF-8

                $curl = curl_init();
                curl_setopt($curl, CURLOPT_URL, $url);
                curl_setopt($curl, CURLOPT_HTTPHEADER, array('Content-Type: application/json;charset=UTF-8'));
                curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
                curl_setopt($curl, CURLOPT_VERBOSE, 0);
                curl_setopt($curl, CURLOPT_HEADER, 1);
                curl_setopt($curl, CURLOPT_CUSTOMREQUEST, "POST");
                curl_setopt($curl, CURLOPT_POSTFIELDS, $json_string);
                curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
                $response = curl_exec ($curl);
                curl_close ($curl);

Is there anything obvious Ive got wrong?

Thanks