Just a word of caution when you are considering using the pixieset plugin with Lightroom....
If you have invested significant time and effort into creating collections and publishing photos to them, you should NEVER uninstall the plugin. Once uninstalled, all the photo assignments you've made across your collections will be permanently lost. After synchronization, you'll only be left with the collection folders themselves, while the collections in Pixieset will show zero images within them.
I recently experienced this issue when troubleshooting a problem with the plugin; thinking a reinstall might help - a fatal mistake! Despite working with pixieset support, there was ultimately no way to recover the image assignments. Once the image assignment associations are gone due to uninstallation, they can never be recovered, and support confirmed this.
In my case, I had hundreds of photos organized across numerous collections. I'm not redoing all that work. Instead, I've uninstalled this plugin and will manage my collections manually, uploading photos directly into the site. It's not as slick of a process, but I'll never lose track of what photos are assigned where again.