PHP can’t see something in its include_path

I’m trying to run PHPMailer on my server, but I’m having trouble getting PHP webpages to find it.

If I run php -f send_mail.php, it runs just fine, but when I curl, I get the following error:

Warning: require(PHPMailer/src/Exception.php): failed to open stream: No such file or directory in /var/www/html/send_mail.php on line 10

Fatal error: require(): Failed opening required 'PHPMailer/src/Exception.php' (include_path='.:/usr/share/pear:/usr/share/php') in /var/www/html/send_mail.php on line 10

I note in the above error that the include path looks to be '.:/usr/share/pear:/usr/share/php', even though in /etc/php.ini, I have the line include_path = ".:/usr/share/pear:/usr/share/php:/php/includes". I also ran phpinfo() to verify that /etc/php.ini was being read by the interpreter, and all seems fine there.

In any case, the PHPMailer folder is in the include_path quoted in the error, so it should be seeing it anyway.

(me@server ~)$ ls /usr/share/php/PHPMailer/  composer.json  examples             language  phpdoc.dist.xml  test           
COMMITMENT    docs           get_oauth_token.php  LICENSE        src          travis.phpunit.xml.dist  VERSION

Any ideas what I might be missing to get PHPMailer visible to my PHP webpages?

EDIT: I’ve also seen this question already, but the problem here seems to be related to a leading backslash in the path given to require, which isn’t my issue.