validate.php

<?php

request()->validate([
    'email' => ['required', 'email'],
    'payment_token' => ValidPaymentToken::class,    
], [
    // messages
]);

// With parameters:

request()->validate([
    'email' => ['required', 'email'],
    'payment_token' => [ValidPaymentToken::class, $param1, $param2],    
], [
    // messages
]);

ValidPaymentToken.php

<?php

use Illuminate\Contracts\Validation\Rule;

class ValidPaymentToken implements Rule;
{
    /**
     * @var \CreditCardGateway
     */
    private $gateway;

    public function __construct(CreditCardGateway $gateway)
    {
        $this->gateway = $gateway;
    }

    /**
     * Determine if the validation rule passes.
     *
     * @param  string  $attribute
     * @param  mixed   $value
     * @return bool
     */
    public function passes($attribute, $value, array $parameters = [])
    {
        $param1 = $parameters[0];
        $param1 = $parameters[0];

        // validate stuff;
    }
    
    /**
     * Get the validation error message.
     *
     * @return string
     */
    public function message()
    {
        return 'custom message';
    }
}