Invalid characters passed for attempted conversion when using base_convert on Codeigniter 4

Question

I have a problem with base_convert function on PHP, I'm trying to make a unique ID for my primary key,

here is my code

base_convert(microtime(false), 10, 36)

but always showing error like this

Invalid characters passed for attempted conversion, these have been ignored 

I'm using Codeigniter 4 with PHP 7.4.29

Answer 1

Thanks for your responses, I already fix it using

$cleanNumber = preg_replace( '/[^0-9]/', '', microtime(false));
base_convert($cleanNumber, 10, 36)