OTP Generate in PhP

$otp = substr(str_shuffle("0123456789"), 0, 4);

$otp = str_pad(rand(0000,9999), 4, "0", STR_PAD_LEFT); // 4 Digit, add "0" if Length is 5 and generate digit is 4

$randomString = substr(str_shuffle("0123456789abcdefghijklmnopqrstvwxyzABCDEFGHIJKLMNOPQRSTVWXYZ"), 0, 11) // string Length 11