This is my setup for trace:

(It's TypeScript - ES6 syntax)

    x: this.users.map((u) => u.followerCount),
    y: this.users.map((u) => u.postCount),
    text: this.users.map((u) => u.username),
    // ...

The rest is just copied off the Colored and Styled Scatter Plot example.

When I run this, error from title is reported: Error: Missing required POST parameters: un key origin.
Although if I remove text: ..., it runs successfully.
I have checked the lengths and they match, all usernames are strings and there is also no falsy values.

Although if I change value mapped value to some fixed string, it runs. I'm unsure why it won't work for dynamic strings.
There are some special characters (emojis, etc.), could this be a problem, same as in #15?

Update 1: removing all non-ascii characters didn't help either. It repots a different error:
Error: Hm... Plotly had some trouble decoding your 'args'. ...
Which is as unhelpful as the first one.

Update 2: using regex [^a-zA-Z] as .replace(/[^a-zA-Z]/g, "") on each name finally worked. This is very dirty hack and I'm disappointed on that I had to use it.