php5-gd not installed error, but it is installed and enabled…

My contact form shows the

ERROR: si-contact-form.php plugin says GD image support not detected in PHP!

Contact your web host and ask them why GD image support is not enabled for PHP.

ERROR: si-contact-form.php plugin says imagepng function not detected in PHP!

Contact your web host and ask them why imagepng function is not enabled for PHP.

but I know GD is enabled.

Results of php -i | grep GD

GD Support => enabled
GD Version => 2.1.1-dev

Does si-contact-form require a specific version of GD?

BTW, I am on the latest update for si-contact-form.

https://wordpress.org/plugins/si-contact-form/