Before you can use the Mailjet REST APIs, you will need to have a valid Mailjet [API key/API secret]. Below are the steps you will need to create a Mailjet API credentials.
Open a browser tab and Log In to your Mailjet Account. Click on your avatar in top right corner. Then click on Account Settings. On the Account Information page, click on “Master API Key & Sub API key management” under the “REST API” section.
Scroll down to the “Master API Key” section and copy the details.