Setting a default value to a signed parameter

I have a dashboard with a card that has a parameter. The dashboard exposes this parameter in an editable way. Then in my application where is embedded the dashboard I sign a json similar to this one:

{
resource: { dashboard: 111 },
params: {}
};
Doing that I was able to embed the dashboard in my app and see a widget for my parameter.
However, if I set a default value for the param on this way:
{
resource: { dashboard: 111 },
params: {"param": "value"}
};

the widget for the parameter disappears.
Is there a way in which I can send from the app a default value for an editable signed parameter keeping its widget in the dashboard?

My metabase version is v0.39.1 because I should use java 8.

We are on 1.49.5 ... i would recommend you upgrade cause rarely anyone remembers 39