"Call to undefined function array_key_last()" although it is a PHP function that works locally

Question

I made a website that works perfectly locally. Now I'm trying to publish it online with ploi.io . I get this error:

"Call to undefined function array_key_last()" 3rd line in code

but array_key_last() is a PHP-function.

https://www.php.net/manual/en/function.array-key-last.php

Here is my website link: http://rocallisa.xyz/

if($key === array_key_last($photos))

My server is running PHP 7.3 but this doesn't help.

Answer 1

What is the PHP version in the online publication?

In PHP docs:

array_key_last (PHP 7 >= 7.3.0)

https://www.php.net/manual/es/function.array-key-last.php

Is the version of your remote server latter than 7.3?

An alternative: How to get last key in an array?