Thank you very much for your support. Two things were new to me :
– need of elevated access
– making it a standalone app
I deleted my old app, followed all you steps and then connected again the plugin to the API. Unfortunately there is again an “Twitter Connection Problem. error code: 403”.
Something else to do ?
One thing changed … in the popup boxes now appears my logo from the twitter account. This was not the case before.
BR Chris