shinyapps.io Error

I have been trying to solve this error for a few days and can not find the correct solution:

I build a prediction app, but every time I include the predict() function (like this:

prediction <- predict(model_knn, test1)[2]
prediction <- round(test12, 4) *100
    
result <- paste( "String", toString(test12), "%", sep = " " )
result
) 

, i get this error: "An error has occurred. Check your logs or contact the app author for clarification."

The error only seems to occur when I use the predict function. My prediction model is 7 MB big and I built it with caret.

The logs:

> 2020-10-16T20:43:27.871025+00:00 shinyapps[3031222]: Running on host: 9442e0c538c5
> 2020-10-16T20:43:27.875663+00:00 shinyapps[3031222]: Server version: 1.8.4.1-20
> 2020-10-16T20:43:27.875673+00:00 shinyapps[3031222]: LANG: de_DE.UTF-8
> 2020-10-16T20:43:27.875697+00:00 shinyapps[3031222]: R version: 4.0.2
> 2020-10-16T20:43:27.875715+00:00 shinyapps[3031222]: shiny version: 1.5.0
> 2020-10-16T20:43:27.875756+00:00 shinyapps[3031222]: httpuv version: 1.5.4
> 2020-10-16T20:43:27.875774+00:00 shinyapps[3031222]: rmarkdown version: (none)
> 2020-10-16T20:43:27.875774+00:00 shinyapps[3031222]: knitr version: (none)
> 2020-10-16T20:43:27.875775+00:00 shinyapps[3031222]: jsonlite version: 1.7.0
> 2020-10-16T20:43:27.875782+00:00 shinyapps[3031222]: RJSONIO version: (none)
> 2020-10-16T20:43:27.875807+00:00 shinyapps[3031222]: htmltools version: 0.5.0
> 2020-10-16T20:43:27.875971+00:00 shinyapps[3031222]: Using pandoc: /opt/connect/ext/pandoc2
> 2020-10-16T20:43:28.030245+00:00 shinyapps[3031222]: Using jsonlite for JSON processing
> 2020-10-16T20:43:28.033232+00:00 shinyapps[3031222]: 
> 2020-10-16T20:43:28.033233+00:00 shinyapps[3031222]: Starting R with process ID: '25'
> 2020-10-16T20:43:28.055897+00:00 shinyapps[3031222]: 
> 2020-10-16T20:43:28.055898+00:00 shinyapps[3031222]: Listening on http://127.0.0.1:44282
> 2020-10-16T20:43:43.378565+00:00 shinyapps[3031222]: randomForest 4.6-14
> 2020-10-16T20:43:43.382406+00:00 shinyapps[3031222]: Lade nötiges Paket: lattice
> 2020-10-16T20:43:43.424411+00:00 shinyapps[3031222]: Lade nötiges Paket: ggplot2
> 2020-10-16T20:43:43.378759+00:00 shinyapps[3031222]: Type rfNews() to see new features/changes/bug fixes.
> 2020-10-16T20:43:43.685336+00:00 shinyapps[3031222]: 
> 2020-10-16T20:43:43.685337+00:00 shinyapps[3031222]: Attache Paket: ‘ggplot2’
> 2020-10-16T20:43:43.685337+00:00 shinyapps[3031222]: 
> 2020-10-16T20:43:43.686047+00:00 shinyapps[3031222]: The following object is masked from ‘package:randomForest’:
> 2020-10-16T20:43:43.686048+00:00 shinyapps[3031222]: 
> 2020-10-16T20:43:43.686048+00:00 shinyapps[3031222]:     margin
> 2020-10-16T20:43:43.686048+00:00 shinyapps[3031222]: 
> 2020-10-16T20:43:45.317834+00:00 shinyapps[3031222]: Warnung: Error in ..stacktraceon..: Objekt 'result' nicht gefunden
> 2020-10-16T20:43:45.323649+00:00 shinyapps[3031222]:   109: isolate
> 2020-10-16T20:43:45.323650+00:00 shinyapps[3031222]:   108: renderText [/srv/connect/apps/cardioapp2/server.R#39]
> 2020-10-16T20:43:45.323651+00:00 shinyapps[3031222]:   107: func
> 2020-10-16T20:43:45.323652+00:00 shinyapps[3031222]:    94: origRenderFunc
> 2020-10-16T20:43:45.323652+00:00 shinyapps[3031222]:    93: output$txtout
> 2020-10-16T20:43:45.323652+00:00 shinyapps[3031222]:    13: runApp
> 2020-10-16T20:43:45.323652+00:00 shinyapps[3031222]:    12: fn
> 2020-10-16T20:43:45.323653+00:00 shinyapps[3031222]:     7: connect$retry
> 2020-10-16T20:43:45.323653+00:00 shinyapps[3031222]:     6: eval
> 2020-10-16T20:43:45.323675+00:00 shinyapps[3031222]:     5: eval

Does anyone know what I am doing wrong?

Thanks in advance!

First question, What defines this ?