Support for PHP 8.x

[xpurichan]

One of the sites that we manage uses your WordPress plugin, which unfortunately does not appear to be fully compatible with PHP 8.x. Two of the Settings tabs for your plugin do not load and cause the following PHP fatal error to be thrown:

PHP Fatal error: Uncaught TypeError: join(): Argument #2 ($array) must be of type ?array, string given in /srv/htdocs/wp-content/plugins/supercast-1.6.0/lib/membership-plugins/memberful.php:99

The root cause is an incorrect call to the join() PHP function (Alias of implode()). The code inverts the array and separator parameters, which causes a warning in PHP 7.4, but a fatal error in PHP 8.x.

While the site we manage is using an older version of your plugin (version 1.6.0), the join() function is still broken in PHP 8 with the latest version of your plugin (version 1.7.4, based on this GitHub repo).

[jonesch]

It looks like you put a check in place to ensure the argument is being passed to join() is an array:
is_array($pair_outputs) ? join($pair_outputs, ',') : $pair_outputs;

But the Fatal Error is still present.

join($pair_outputs, ',') needs to be converted to join(',' $pair_outputs), putting the Array as the second argument: Source https://www.php.net/manual/en/function.implode.php