Magento1.9 - AWS SES not working with Magento1.9 SMTP extension

Question

I'm getting the below error message while sending an email using Amazon SES in Magento1.9.2.4(Aschroder SMTPPro extension).

I'm using the same credentials in Magento2.3(Mageplaza SMTP extension) which are working.

I think the below code is used to get authentication key:

<?php
private function _buildAuthKey($date){
    return sprintf('AWS3-HTTPS AWSAccessKeyId=%s,Algorithm=HmacSHA256,Signature=%s', $this->_accessKey, base64_encode(hash_hmac('sha256', $date, $this->_privateKey, TRUE)));
}
?>

Thank you.