1👍
You might want to try representing the "paid status" as a numeric (0-unpaid, 1-paid) then use a callback to customize the tooltip:
function(tooltipItems, data) {
var y = tooltipItems.yLabel;
if(tooltipItems.datasetIndex === 1) {
tooltipItems.yLabel === 0 ? y = 'unpaid' : y = 'paid'
}
return y
}
}
Source:stackexchange.com