Hi Cornelius, there is much to learn to get a nonlinear model to converge. Please use File Archive to save a .wbpz file. Put that file (not the .wbpj file) on a file sharing site like Google Drive or OneDrive. Make sure to set the permissions so that anyone can download the file. I will take a look.
There are tutorials on nonlinear convergence and several questions on the forum on this topic.
Here is a Google Search result for the phrase “unable to converge” in this site, but nothing older than 3 years. Some older results have broken links that will land you on the home page.