With a two-way sync group, you can sync versions across a group of Jira projects. We usually recommend the two-way sync because it covers most of the use cases.
Use Case: If you have e.g. three different teams (Dev, Marketing, QA) which work on the a software product and contribute to the same releases, you create a two-way sync group which contains all projects.
Go to Version Sync in Project A: Project A > Project settings > Apps > Version Sync
Make sure that you are in the tab Two-way sync
Create a new group (e.g. PA) with default settings
Click + Add another project
Select the project you want to add to the sync group (e.g. Project B)
> You get redirected to the Version Sync settings of Project B
Make the desired settings and save
If applicable, sync existing versions from Project B manually
Future version will be synced automatically.