How to call function from custom helper ?

rename your file to i.e. myDate_helper. Save it in the App\Helpers folder.
I don't think it is necessary to namespace the file, I usually don't do that.

Before calling the method formatDateTime(), add the following line before calling it:

PHP Code:

helper('myDate'); 


Now you can call your method by using:

PHP Code:

$test = formatDateTime($params); 


Also check out: https://stackoverflow.com/questions/6188...eigniter-4