Fatal error: Call to undefined function imap_open() in PHP

This error message indicates that the PHP script you are running is trying to use the imap_open() function, but it is not defined or not enabled in your PHP configuration. imap_open() is a function that is used to open a connection to an IMAP (Internet Mail Access Protocol) server, so it is likely that your script is trying to access an email account.

To resolve this issue, you will need to make sure that the IMAP extension for PHP is installed and enabled on your server. This can typically be done by installing the appropriate package for your operating system and then enabling the extension in your PHP configuration file (usually called php.ini).

For example, on Ubuntu or Debian, you can install the PHP IMAP extension by running the following command:

sudo apt-get install php-imap

And then you need to check if the extension is enabled in your php.ini file.

;extension=imap

Remove the semicolon in front of the line to enable the extension.

After you have done this, you will need to restart your web server for the changes to take effect.