Make the book a shared one
Open the book and go to the members view. If the book is still local, GoodShare offers to upload it. You need an account for this — a local book cannot be shared.
Invite a member
"Invite member" produces an invitation. You can send the link through any messenger, or pass on the code it shows.
The other person joins
Tapping the link opens GoodShare (and the Play Store first, if the app is not installed yet). After signing in, the book appears in their list. From then on, every entry either of you records syncs to the other.
Frequently asked questions
No. And if you have GoodShare Pro, everybody in your shared book gets the Pro features while they are a member.
There is no fixed limit. Couples, flat shares and families are the common cases; club treasuries with more members work too.
Yes, in the members view. Their entries stay in the book, so past settlements remain correct.