Private purchases paid for with business account

I've had this happen to me a lot, but it's not total because you can just transfer money from your private account to your business account.

Thanks for your answer. Do I need to enter this in Dextter?

Since you don't have double-entry bookkeeping, you don't need to enter anything. Refunding is not necessarily required, but it does leave a clear trail from the mistake, which is more than enough to justify it, if necessary, of course.