Attribute spend to clients or projects with rules, not spreadsheets.
Tags
A tag is a name and a colour you attach to an API key or a project, on the Tags screen. Every event that key produces inherits it, backwards as well as forwards, so tagging today fixes last month too. Freelancers tag by client; teams tag by product area. Tags flow through the ledger, exports and the weekly digest.
A key can carry more than one tag, so a key shared between two clients belongs to both. That does mean spend-by-tag rows can add up to more than the workspace total; the Tags screen says so when it happens, and the total is always each event counted once.
Per-tag invoicing
The tag invoice export produces a client-ready CSV of one tag's spend for a period, the freelancer's pass-through billing sheet.