Mersal Billing Against Money You Already Hold
Held, Not Earned
A retainer is money in your custody. It is not revenue. Until you do the work that draws it down, it belongs to the client, and the client can ask for it back. This distinction is the entire discipline. Treat the balance as a liability, not as a receivable you have already collected, and most of the errors that follow will not occur.
The temptation is to see a funded account and bill against it loosely. That is how trust money and firm money begin to mix. The remedy is procedural: every draw is a discrete, dated, described event, and the running balance is always visible to both sides. A retainer statement is not an invoice. It is an accounting of someone else's money that you are permitted to touch only as you earn it.
The Drawdown Must Be Legible
When you apply held funds against a bill, three parties need to agree on the arithmetic: the lawyer, the client, and the books. A drawdown that only the firm can see is not a drawdown. It is a private adjustment, and private adjustments are what auditors reconstruct after the fact.
Legibility means each application shows the work performed, the amount taken, and the balance that remains. It means the client can open the same ledger you keep and reach the same number. Consider a matter opened with a deposit of 4,000 against which three tranches of work are drawn over a quarter: each draw should read as its own line, timestamped, leaving a balance no one has to compute by hand.
In Mersal, retainer billing runs draw against the held balance on the matter, and the client sees invoices and sealed receipts in the portal, each acknowledged server side.
Never Mixed With Fresh Receivables
The second rule is separation. Held funds and new billing are different instruments and must not share a serial or a stream. When you invoice for work beyond the retainer, that invoice is a fresh receivable with its own number in its own book. When you draw down the retainer, that is a movement against custody. Collapsing the two produces statements no one can trust and books no one can audit.
Serial discipline enforces the wall. Many VAT regimes require sequential, unbroken invoice numbering precisely so that nothing can be inserted, removed, or double-counted. A held-funds movement and a taxable invoice living in one uninterrupted series is the accounting equivalent of an unlocked door. Keep the books apart, and reconciliation stops being an investigation and becomes a glance.
Billing against a retainer is a test of custody more than a test of billing. If the client can see every draw, if the books reconcile without a story, and if held money never touches fresh receivables, you have honored the trust the deposit represents. The firm that gets this right is not merely tidy; it is defensible on the day someone asks where the money went. Hold the line, and the line holds you.
Matters, conflicts, VAT billing, sealed receipts and the docket, in one defensible system.