To export both a Lightroom Catalog and Smart Previews, open your catalog in Lightroom.
Open the catalog you'd like to send me in Lightroom and select the images you'd like us to edit (if you have any image you've already edited, please select those as well and label them in green so I can use them as editing reference. You can do this by right clicking on the image and selecting 'Set Color Label', then select 'Green'.
Then go to 'File' in the upper left of Lightroom.
Once you're in the 'File' tab, go down to 'Export as Catalog'. A window should pop up, go ahead and name the catalog (I recommend your client's name and your studio name).
At the bottom of this window, you should see 3 or 4 check boxes. In the export process within Lightroom Classic, make sure that you choose the "Build/Include Smart Previews" option ONLY. Do not check "Include available previews".
This results in the creation of two files in the folder you'll zip and send me: the .lrcat file (the Lightroom Classic catalog), and the .lrdata file (the Smart Previews).
Select the folder that contains your Lightroom Catalog + Smart Previews, right-click the folder, and select "Compress Items" if you're on a Mac/Apple. If you're using Windows you'd right-click the folder and select 'Send to' and then select 'Compressed (zipped) folder'.
Take the newly created zipped folder and upload it to either Dropbox, WeTransfer (wetransfer.com), or Google Drive. You can then email this link directly to me.