REST V1/customers adding a new extension attribute Magento 2.3.1

I have added a new field as “is_seller” in registration page (same as “is_subscribed). If the checkbox is clicked the customer Id will be saved to another table with some additional values.

It was done through the event. But using v1/customers how can I achieve this.
When I tried to add it thorugh the parameters as below

"customer": {
        "email": "[email protected]",
        "firstname": "test,
        "lastname": "test",
        "store_id": 1,
        "website_id": 1,
        "is_seller":1
    },
     "password": "Password1"

I am getting the following error

Message: Property “IsSeller” does not have accessor method
“getIsSeller” in class “MagentoCustomerApiDataCustomerInterface”.

I tried using extension attributes also, but it is not working.