Can several servers share the same balances?

#Answer

Yes. Point every server at the same MySQL or MariaDB database in config.yml. Every change is written so that two servers changing the same balance at once lose nothing, and a payment another server already spent is refused.

Each server keeps the balances of its online players in memory. Turn on the Redis sync to have the other servers pick up a change straight away. Give each server its own server name if some currencies should only work on some of them.