In your json structure, add a “name” element for each trace, something like this:
[
{
"name": "Sales",
"x": [ 1, 2 ],
"y": [ 1, 2 ],
"type": "scatter"
},
{
"name": "Expenses",
"x": [ 3, 4 ],
"y": [ 9, 14 ],
"type": "scatter"
}
]