please explain bit more detail what is your use case what you are trying to achieve, what is your tridion version etc.

Error looks System.Text.Json assemply version is missing, could be pre-requisites are not installed. also update provide details of which version of tridion sites etc

Welcome to tridion stackexchange. Could you please update and provide trace logs details of the error. maybe you can find it in the event viewer in the Tridion Sites installed server.

Is that your cms setup endpoint uses https?

question is not bit clear, what type of add-on extension? are you looking for add-on package extension to be enabled or disabled in add-on service? or for example add-on extension to enabled and deployed in CME and then only to be make an http request to that url and enable the extension depending on the result.