What is double-entry in a ledger?

Double-entry means every transaction has two sides: a debit and a credit of the same amount. In product language those sides are source and destination. The book stays balanced because you never post one side alone. A fee, a deposit, and a refund all use that pair.

How does double-entry work?

You pick two accounts. One goes down. One goes up. The amounts match. A deposit, a fee, and a refund are all the same shape. If you need three accounts, you post two transactions or a split whose legs still sum to zero.

Debit vs credit

Debit and credit are the accounting names for the two sides. Which side increases an account depends on the account type. Source and destination skip that vocabulary. They name the path of the money. The posting is still double-entry.

Why not single-entry?

A single-entry book adds and subtracts on one list. It cannot tell you where the money came from. When a wallet and a fee account disagree, you have no second side to inspect. Double-entry makes that disagreement visible on the same day you post it.

Blnk implements double-entry as a required source and destination on every transaction. There is no one-sided credit API. Read double-entry for developers for the walkthrough, then post against the map.