Property label

The label property is used inside link blocks and should hold the text you have to click to be redirected to the configured link.

{
    "from" : "info@example.com",
    "subject" : "Email with a single link",
    "content" : {
        "blocks" : [ {
            "type": "link",
            "label" : "Responsive email",
            "link" : "https://responsiveemail.com/"
        } ]
    }
}

For more information and more examples, please check the documentation of link blocks.