call to undefined function sendgrid curl_init

The SendGrid\curl_init prefix is misleading: this is not a SendGrid or SMTP error code. It is a standard PHP fatal error raised because the sendgrid-php library tries to call curl_init() and PHP's cURL extension isn't loaded.

Why does the error say SendGrid\curl_init() instead of curl_init()?

SendGrid's HTTP layer lives in a namespace. When PHP resolves an unqualified function call inside a namespace, it first looks for SendGrid\curl_init, and only falls back to the global curl_init if the function exists. When ext-curl is not loaded, no global curl_init exists, so the fallback fails and PHP reports the name it tried first — the namespaced one. You'll see it surface here:

Fatal error: Uncaught Error: Call to undefined function SendGrid\curl_init()
in .../vendor/sendgrid/php-http-client/lib/Client.php:459

So the namespace prefix is a red herring — the real problem is always a missing/disabled cURL extension. (Confirmed in sendgrid-php issue #811.)

What causes "Call to undefined function SendGrid\curl_init()"?

sendgrid/sendgrid depends on sendgrid/php-http-client, which uses cURL for every API call — ext-curl is a hard requirement declared as "ext-curl": "*" in its composer manifest. The error means one of:

• The cURL extension is not installed for your PHP at all.
• It's installed but commented out in php.ini.
• It's enabled for one SAPI but not the one running your code. A very common trap: cURL is enabled for PHP-CLI but not for the Apache/PHP-FPM module serving your site (or vice versa). PHP-CLI and the web SAPI can use different php.ini files.
• On Windows: an architecture/build mismatch between PHP, the web server, and the extension DLL.

How do I fix "Call to undefined function SendGrid\curl_init()"?

1. Confirm which PHP is missing cURL. Check the exact runtime that throws the error, not just CLI:

<?php
var_dump(extension_loaded('curl')); // false = the problem
echo php_ini_loaded_file();         // tells you which php.ini that SAPI uses

Or from the shell for the CLI runtime:

php -m | grep -i curl

2. Install / enable the extension.

Debian/Ubuntu (match your PHP version):

sudo apt-get install php-curl       # or php8.2-curl, etc.

RHEL/CentOS/Alma:

sudo yum install php-curl

Windows / manual php.ini — remove the leading semicolon:

extension=curl       ; modern PHP (Linux build often: extension=curl.so)
;extension=php_curl.dll   -> extension=php_curl.dll   (older Windows)

3. Restart the SAPI that serves your app — this is the step most often missed. Editing php.ini does nothing until you reload the process:

sudo systemctl restart apache2     # or: php8.2-fpm, nginx-fpm, httpd

4. Re-verify extension_loaded('curl') returns true in the same SAPI, then re-run your SendGrid send.

If you installed sendgrid-php manually instead of via Composer, switch to composer require sendgrid/sendgrid — Composer validates the ext-curl requirement at install time and surfaces the missing extension before runtime.

On managed/shared hosting where you can't edit php.ini, ask your host to enable cURL for your account (often toggleable in cPanel under "Select PHP Version" → Extensions).