Retainers are the best income a freelancer has and the dullest paperwork. Every month you open last month's invoice, copy it, change the month, change the number, and send. In a busy month you forget. In a forgotten month, you get paid two weeks late.
Here's how to make it happen without you in MANA.
Three things to prepare first
1. Your sender profile. Fill it in completely before issuing anything — the legal name and address you actually use, your taxpayer ID, VAT registration status, and the PromptPay details clients pay into. If you're not VAT-registered, leave that flag off; turning it on produces the wrong document type.
2. The client contact. Use the company name as registered, the taxpayer ID, the billing address, and the accounts payable email — not the email of the person you chat with about the work. This is where invoices most often disappear: sent to someone with no authority to pay them.
3. A clear agreement. Before automating anything, know the billing date, the payment terms, what's in scope each month, and how out-of-scope work is charged. Automation takes a vague agreement and turns it into a monthly argument.
Setting it up
1. Build one template invoice properly
Create a new document, choose invoice, attach it to that client's contact and project, and write the line items in more detail than feels necessary.
Instead of "Monthly service fee — THB 30,000", write "Monthly maintenance and design retainer per agreement dated 1 March 2026, covering up to 20 hours".
The reason isn't tidiness. It's that when your client's finance staff changes, the new person reads the document and understands what they're paying for without asking you.
2. Get the tax right in the template
Set the withholding rate on the document. For services billed to a Thai company that's typically 3%, and if you're VAT-registered you add 7% on top. The order matters: VAT is added to the fee; withholding is calculated on the fee before VAT, not on the gross total.
A THB 30,000 retainer, VAT-registered, corporate client:
- Fee: 30,000
- VAT at 7%: 2,100 — total 32,100
- Withholding at 3% of 30,000: 900
- Client transfers 31,200 and issues you a withholding tax certificate for 900
Set it once in the template and every month calculates identically.
3. Turn on recurring generation
Set the cycle to monthly and pick the generation date. The recommendation: generate one or two days before you actually need to send, so you get a review window rather than an immediate send.
Almost every retainer month has an extra — out-of-scope work, a licence you fronted, a long holiday week. A draft waiting for your check beats an invoice already sent that now needs a credit note.
4. Confirm the dates appear on your calendar
Open the calendar and enable the document deadline layer. You'll see invoice due dates and recurring generation dates sitting next to your tasks and milestones on one screen.
People skip this step, and it's the step that makes the system work. Seeing a due date coming is what gets you messaging a client before it passes rather than after.
5. Check the first cycle by hand
The month after you set it up, open the generated draft and read it line by line — sequence number, billing period, amounts, recipient address. Two minutes, and the most valuable two minutes in the whole process.
Close the loop after sending
- Record the payment when money lands. Don't leave paid invoices sitting in your overdue list — a false overdue list is one you stop reading entirely.
- Issue the receipt. Corporate clients need it to close their month, and you need it at year end.
- File the withholding certificate. Put the certificate number on the document and attach the file. That THB 900 a month is THB 10,800 a year you can credit or reclaim — if you have the paperwork.
What automation won't fix
Recurring documents solve retyping. They don't solve a client who pays late. If the same client is overdue every month, the problem is their payment terms or their internal process, not your tooling.
They also don't solve scope creep. If you delivered 40% more work this month and billed the same number, automation just helped you lose money punctually and consistently.
Spend the time you saved checking that the number on the invoice still matches the work. That's the part no tool does for you.