Warning in install.packages : package ‘NonlinearTSA’ is not available (for R version 3.5.1)

Now you are having connectivity issues, R is not being able to connect to the CRAN repository you have selected, these are some things to try.

  • Choose a different CRAN repository, RStudios repository is a good choice (http://cran.rstudio.com/) or you could choose one that is geographically closer to you.
  • Disable secure download setting.
  • Check if your internet connection has traffic restrictions of some kind, like a firewall, proxy server, etc. This is usually the case when you are at work or school.

But, I also agree with @Timesaver, you should consider updating your R version, at will make things easier for you in general.

Note: Please do not post screenshots, they are considered a bad practice here, post the console output as formatted code instead, here is how to do it: