Sync Calibre Library on DropBox to SDHC on LG V20 cell phone

[lancre]

I'm not sure where to put this. If this is the wrong spot, please point me to the right one.

In Windows, I've placed my Calibre Library in E:\Users\Dropbox\Calibre Library, E: being my data drive. This way, as soon as I add an ebook to Calibre, it gets backed up to Dropbox, where I can access it from any place.

In the past I've used CalibreBox on my LG V20 android phone to browse and download ebooks from Dropbox when I'm on the road. Unfortunately, recently Dropbox and CalibreBox seem to have stopped communicating.

So I looked for an alternative and settled on CalibreSync.
Space is limited on the phone's internal storage but I have a 128G SDHC card inserted. I would like to have the program sync my Calibre Library to the SDHC to save space on the internal memory.

CalibreSync doesn't seem to want to sync to the external SDHC, and CalibreBox doesn't want to connect at all. Can anyone here offer a workaround for either app, or suggest a different one that will let me browse from my phone and sync to the SDHC?

Thanks.