Login to geocaching in Locus is possible only in Locus Pro (if we do not count a testing version of Locus Free). Every feature that require geocaching live, should open a window with login options. Such window should not be visible in Locus Free so there is no option to login at all.

for me it is possible only with FREE

My situation,
at the moment i have installed
official Locus Free and Promy workflow:
- i log out PRO from GS and close PRO
- i reset FREE preferences, start it, download additional data
- i create a offline log with FREE
- now i open "FieldNotes" and proceed "upload Fieldnote"
with FREE- login to GS with successfull upload of this fieldnote
see attached video
- while opening my account on PC i see this uploaded fieldnote

- to verify i open PRO > i am furtermore logged off on GS