Error installing loadflex on Mac for R version 3.5.2

Hi,
I'm getting an error trying to install the loadflex package, shown below.

```
ERROR: dependencies ‘rloadest’, ‘smwrQW’ are not available for package ‘loadflex’
* removing ‘/Users/####/Library/R/3.5/library/loadflex’
installation of package ‘/var/folders/23/1ys3hzvj0z31wxkmz5gr_6dh0000gn/T//RtmpknegvN/filec086fd454ae/loadflex_1.9.1.tar.gz’ had non-zero exit status
```

I have tried solutions posted on some similar threads (https://github.com/USGS-R/loadflex/issues/212), as well as the FAQs page (https://github.com/USGS-R/loadflex/wiki/Installation-FAQ), but have had no such luck with any solutions. (I continue to get the same error, saying it is not available for the most recent version of R.)

Any help is appreciated! Thanks so much!