How to create object in server action?

I need an object like this:

{
"email@email.com": {"ref_id":"999"}
}

Where the email and the ref_id values are variables.

So I have successfully created this object with this set value:

{{
{email@email.com:{ref_id:999999}} 
}}

But my issues come when trying to place my variables:

• This doesn’t work:
  it simply makes “to_email” a string:

I feel like this is much harder than it should be. Hopefully I’m missing something.
Please help