Back up your site. An import can be undone, but a backup is quicker if something unexpected happens.

PaddleSubs must be online: Offline Enabled off, and an API key for the current Environment. All imported access is attached to a price in Paddle, and the wizard may create new products and prices there. It refuses to start otherwise.

Choose the environment on purpose. The wizard says which one it imports into. Importing into the sandbox is a full rehearsal, kept apart from production; see the section called “Rehearsing in the Sandbox”.

You need the Import from another system permission, which Super Users have.

Have a copy of the old system's data: a database dump (.sql or .sql.gz) of the old site, or a database login that can read it.