Problem with sluggable cyrillic symbols with iconv()

Question

I try to transliterate cyrillic words using iconv php function.

$s = 'Електроінструмент';
$s = iconv('UTF-8', 'ASCII//TRANSLIT', $s);

But i always get

Notice: iconv(): Detected an illegal character in input string

How i cat to solve this problem?

I use php 7.4, symfony 5 and Ubuntu 20 server. This iconv function using in KNP Sluggable bundle for symfony.

Answer 1

Update to symfony 5.0 fixed it.