振り替え vs. 振り込む: What's the difference?

The meaning differs slightly by the financial institution.

「振替」refers to the transfer between the bank accounts of the same person.

「振り込み」 means to remit money to others.

「替」 here means "replacement." In essence, the person's property has not increased, but the amount of money in different accounts has been replaced. So "「振替」" is not difficult to understand.