Hi @CaseyWen,
Normally you can specify the value for each field in the Create Item. With this approach it is unable to load these fields and will only show the item field. Within that item field you need to specify which fields you want to set and the values (with valid json).
You are only setting a value and you are not specifying any field for that value, which makes it invalid json for the item field.
Below is some example json for creating an item where the title column will have the xx value.
{
"Title": "xx"
}
