A transaction line is a record of a transaction between your business and a trading partner. This record contains key details such as the date of the transaction, the number of units sold, their value and the currency used.
Along with these key details, a number of dimension items can be related to a transaction line. This can allow each record to have an associated product, branch, and other configured items. These dimension items will then be used to determine which program lines are affected by the transaction line.
Transaction lines can be imported into the system via a CSV upload under Config > Import transactions.
You can see more on transaction lines here.