S8 - Can't import vcard file

[lathe man]

I have a new S8. I was able to use Smart Switch to move contacts from my old phone. Now I want to also import contacts from Thunderbird. I saved Thunderbird contacts as a vcard file and copied that file to the phone. When I try to import that vcard contact file, I get a message about unable to import vcard.

Is the Thunderbird vcard format incompatible?
Is it unable to merge once there is an existing set of contacts?
Is there a better way to get Thunderbird contacts into my S8?

Thank you for your help.