src/EB/SDK/Webhook/Payload.php
public function jsonSerialize()
    {
        return [
            'ip_address' => $this->getIpAddress(),
            'action'  => $this->getAction(),
            'campaign_id' => (int)$this->getCampaignId(),
            'list_external_id' => $this->getListExternalId(),
            'reason' => $this->getReason(),
            'recipient_email_address' => $this->getRecipientEmailAddress(),
            'hash' => $this->getHash(),
            'recipient_external_id' => (string)$this->getRecipientExternalId(),
            'trigger_date' => $this->getTriggerDate()->format('Y-m-d h:i:s'),
            'type' => $this->getType()
        ];
    }
public function jsonSerialize()
    {
        return [
            'ip_address' => $this->getIpAddress(),
            'action'  => $this->getAction(),
            'campaign_id' => (int)$this->getCampaignId(),
            'list_external_id' => $this->getListExternalId(),
            'reason' => $this->getReason(),
            'recipient_email_address' => $this->getRecipientEmailAddress(),
            'hash' => $this->getHash(),
            'recipient_external_id' => (string)$this->getRecipientExternalId(),
            'trigger_date' => $this->getTriggerDate()->format('Y-m-d h:i:s'),
            'type' => $this->getType()
        ];
    }
(PHP 5 &gt;= 5.4.0)<br/>
Specify data which should be serialized to JSON
@link http://php.net/manual/en/jsonserializable.jsonserialize.php
@return mixed data which can be serialized by <b>json_encode</b>,
which is a value of any type other than a resource.