Write up from my comment:
The way to specify an array of strings in mongoose is like so:
var personSchema = new mongoose.Schema({
tags: [{
type: String
}]
However, the problem here is most-likely to do with Postman as it is sending the ‘array’ as a string. You can check this by checking the type of req.body.tags like so:
console.log(typeof req.body.tags)
If this returns a String, make sure to set the content-type in Postman to JSON as seen in this screenshot rather than the default ‘form-data’ option.