Here is my error message in the logs of shinyapp.io. I am trying to launch a data visualization app, but cannot overcome this error. Any ideas?

I am working on a Shiny app and have it nearly done except that one of my download buttons isn’t getting through to the downloadHandler and just downloads an HTML file of the shiny app itself. The project is big so here are, I think, the relevant parts. First, the UI has two tabs. One tab has two download buttons, the other had one. The two download buttons on the first tab work fine, but when I try to replicate their code on the second tab, I run into this problem. I have confirmed that if I remove the first tab, the button works.

I have made a shiny app and trying to run as an external application, with the app I should be able to generate plot and download them, its working locally on my pc but when I create it as an app and try running it its not downloading and showing an error file.