Changing parameters through rest api

Hello,

I could use a helping hand getting started using the PBI rest api.

I would like to change the value of a pre-defined parameter. I have tried following the steps shown in the documentation:

https://docs.microsoft.com/en-us/rest/api/power-bi/datasets/updateparameters

This is what I tried:

And this is the error I got:

The Parameter DefaultHeatOnValue already exists. I am not very experienced in using api's in general, and I am having some difficulty understanding what the error might be. I am registered as Power BI administrator in my organization.

Cheers and thanks in advance,

Mike