Please go the API Key Management Page to double check you are using the correct API Key and Secret Key.
Then confirm you are using a sender address that is validated on that API Key. (If you are using a subaccount API Key with your PrestaShop integration, please remember to switch to your subaccount in Mailjet before checking the Sender Address page).
If you have confirmed the above information and continue to have an issue, please contact our Support Team with the following information:
1. The PrestaShop version and the PHP version
(From the PrestaShop Admin, click Advanced Parameters → Confirmation Information)
2. The Mailjet plugin version
3. Outline the steps you followed to install the plugin
4. A screenshot of the error message
If you have confirmed the above information and continue to have an issue, please contact our Support Team with the following information:
1. The PrestaShop version and the PHP version
(From the PrestaShop Admin, click Advanced Parameters → Confirmation Information)
2. The Mailjet plugin version
3. Outline the steps you followed to install the plugin
4. A screenshot of the error message