Can I sync my transactions for the last year or more with Synder?

Yes, you can synchronize your old transactions with Synder, just make sure you are subscribed to the plan that allows for historic data import (however, there might be some limitations in your payment provider on how far back you can import data from your platform to Synder). As long as you have transactions in your sales platform you can synchronize them into your accounting system any time if you click the Import Historical Data tab and specify the time range needed. Check out this guide for more details