pfSense

The offending file is:
/etc/inc/dyndns.class

pfSense has the ability to edit files from the webpage GUI (Diagnostics Menu -> Edit File), so just change the existing case statement about half-way through the file, save and you're good to go. I'm not going to check-in changes, I'll leave that to others, sorry.

case 'dnsimple':
                    /*
                    Uses DNSimple's REST API. IP address and TTL sent as JSON, everything else encoded into HTTP Header or URL.
                    Documentation: https://developer.dnsimple.com/v2/zones/records/

                    EXAMPLE: UPDATE a Zone Record.

                    PATCH /:account/zones/:zone/records/:record

                    curl  -H 'Authorization: Bearer <token>' \
                          -H 'Accept: application/json' \
                          -H 'Content-Type: application/json' \
                          -X PATCH \
                          -d '<json>' \
                          https://api.dnsimple.com/v2/1010/zones/example.com/records/5
                    */
                    $needsIP = TRUE;
                    $server = 'https://api.dnsimple.com/v2/';
                    $jsondata = '{"content":"' . $this->_dnsIP . '","ttl":"' . $this->_dnsTTL . '"}';
                    curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "PATCH");
                    curl_setopt($ch, CURLOPT_HTTPHEADER, array('Accept: application/json', 'Content-Type: application/json', 'Authorization: Bearer ' . $this->_dnsPass));
                    curl_setopt($ch, CURLOPT_URL, $server . $this->_dnsUser . '/zones/' . $this->_dnsHost . '/records/' . $this->_dnsZoneID);
                    curl_setopt($ch, CURLOPT_POSTFIELDS, $jsondata);
                    break;

PR URL: https://github.com/pfsense/pfsense/pull/3946