Laravel str_random() or custom function?

you can use this

use Illuminate\Support\Str;

$random = Str::random(40);

str_random (Str::random()) tries to use openssl_random_pseudo_bytes which is a pseudo random number generator optimized for cryptography, not uniqueness. If openssl_random_pseudo_bytes is not available, it falls back to quickRandom():

public static function quickRandom($length = 16)
{
    $pool = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

    return substr(str_shuffle(str_repeat($pool, 5)), 0, $length);
}

In my opinion quickRandom code is not reliable for uniqueness nor cryptography.

Yes, having openssl_random_pseudo_bytes and using 32 bytes is almost impossible to see a collision, but it's still possible. If you want to make sure your strings/numbers will be unique (99.99%), you better use a UUID function. This is what I normally use:

/**
 * 
 * Generate v4 UUID
 * 
 * Version 4 UUIDs are pseudo-random.
 */
public static function v4() 
{
    return sprintf('%04x%04x-%04x-%04x-%04x-%04x%04x%04x',

    // 32 bits for "time_low"
    mt_rand(0, 0xffff), mt_rand(0, 0xffff),

    // 16 bits for "time_mid"
    mt_rand(0, 0xffff),

    // 16 bits for "time_hi_and_version",
    // four most significant bits holds version number 4
    mt_rand(0, 0x0fff) | 0x4000,

    // 16 bits, 8 bits for "clk_seq_hi_res",
    // 8 bits for "clk_seq_low",
    // two most significant bits holds zero and one for variant DCE1.1
    mt_rand(0, 0x3fff) | 0x8000,

    // 48 bits for "node"
    mt_rand(0, 0xffff), mt_rand(0, 0xffff), mt_rand(0, 0xffff)
    );
}

It generates a VALID RFC 4211 COMPLIANT version 4 UUID.

Check this: https://en.wikipedia.org/wiki/Universally_unique_identifier#Collisions