The default escape character was "\\", not '\\'. I believe '\\' is two backslashes, rather than one.

see https://3v4l.org/snSLh or https://github.com/laravel/framework/blob/2d0d6f5f72272a0a0999a10ad12b18fd6564ccc9/src/Illuminate/Validation/ValidationRuleParser.php#L298

The same approach in the PHP documentation. https://www.php.net/manual/en/function.str-getcsv.php#refsect1-function.str-getcsv-examples

I use the same escape character as well, I just wanted to make you aware that this changes functionality.

Edit: TIL, '-strings do some escaping too.

'\n' => \n
"\n" => line break
but
'\\' => \
"\\" => \

So it doesn't actually change functionality because php has a weird, inconsistent escaping mechanism with single quote strings, where backslashes escape only ' and \ characters, but are otherwise interpreted as literal characters.