Using $this when not in object context

[mohammadmehdirezaei]

در این آدرس
callback?Authority=00000000000000000000000000000073123&Status=OK
با خطای زیر
Using $this when not in object context
روبه رو میشم

• Version used (e.g. PHP 7.3 , Laravel 8.65):

vendor\shetabit\multipay\src\Payment.php:139

/**

 * Set payment amount.

 *

 * @param $amount

 * @return $this

 * @throws \Exception

 */

public function amount($amount)

{

    $this->invoice->amount($amount); 
    return $this;

}