In Malaysia, you cannot invoice B2B customers without first confirming they have a valid Service and Sales Tax (SST) registration number—or that they're exempt. The Malaysian tax authority (LHDN) requires this match when you submit to MyInvois , the e-invoice portal. Get it wrong, and your invoice rejects at submission. Get it right, and you avoid audit risk and late invoice acceptance. WhatsApp is where most Malaysian sellers first contact buyers. If you're collecting SST IDs there, you need a process that validates them against LHDN records before your accounting software ever sees the invoice. This post walks through that workflow and shows exactly what breaks when you skip it. Why SST ID collection matters before invoicing MyInvois rejects invoices if the buyer's SST ID doesn't match LHDN's registry. A rejection doesn't just slow cash flow—it signals to your buyer that their tax record is incomplete or mismatched, which delays their own deduction claims. In B2B, that friction kills repeat business. The second risk is simpler: if you invoice without an SST ID match and the buyer claims exemption (say, they're a government body or NGO), you've just created a compliance liability. LHDN can flag the invoice as non-compliant, and you lose the ability to recover input tax. Most sellers using WhatsApp to reach buyers don't have a formal handoff between first contact and invoicing. A message comes in asking for a quote, you reply with a price, the buyer agrees, and then you invoice. At no point do you stop to validate their SST status. That's the gap this workflow fixes. The WhatsApp-to-CRM-to-invoice workflow Here's the step-by-step: Buyer initiates on WhatsApp. They ask for a quote or place an order. Your team receives this message in your unified WhatsApp inbox . Create or link a contact record. Before you reply, create a new contact in your CRM or link to an existing one. Add the buyer's name, phone number, and company name. Send an SST ID collection message. On WhatsApp, ask the buyer for their SST ID. The message should be direct: "Please share your company's SST ID so we can raise the invoice. If you're tax-exempt, please confirm that instead." Have a standard template ready. Record the SST ID in the contact record. When the buyer replies, paste their SST ID into a dedicated field in your CRM contact. Don't leave it in the chat thread—it vanishes in the noise. Validate against LHDN before invoicing. Before you create an invoice, cross-check the SST ID against LHDN's online registry (LHDN provides a lookup tool at lhdn.gov.my ). If it matches and is active, proceed. If it doesn't match or is expired, message the buyer again and ask them to verify with their accountant. Lock the SST ID when you invoice. Once you've validated it, flag the contact record as "SST verified" and include the ID in the invoice details before submission to MyInvois. Your accounting software should pull this from your CRM so there's no re-entry. The key constraint: do not invoice without validation . WhatsApp gives you speed; your CRM gives you a memory. The gap between them is where SST IDs get lost. What happens when you invoice without SST match Let's walk through a real failure case: A Kuala Lumpur distributor sells packaging materials via WhatsApp. A buyer (a food manufacturer in Johor) places an order. The seller creates the invoice immediately, using the buyer's name as it appeared in the WhatsApp message, but doesn't ask for an SST ID. The seller submits to MyInvois. MyInvois rejects the invoice. No SST ID on file. The seller goes back to WhatsApp and asks the buyer for their SST number. The buyer replies: "It's RM00123456789XYZ." The seller updates the invoice and resubmits. This time it passes, but the buyer has now been waiting 2–3 days for an invoice they need to claim input tax on their own returns. They may not use the seller again for a second order. Worse: if the SST ID doesn't exist or belongs to a different company, MyInvois still rejects it, and the seller is now chasing the buyer for a third time to correct the error. The buyer, meanwhile, has flagged the invoice as unresolved in their own accounting software. Multiplied across 50 invoices a month, this friction compounds—and audit risk rises if even a few invoices remain unmatched. The cost of skipping validation is not just a delay. It's also compliance: if you invoice someone with a mismatched or missing SST ID, LHDN may challenge you during an audit and deny the deduction. You absorb the tax cost, not the buyer. Automating SST collection and validation If you're invoicing 20+ B2B customers a month, manual lookups become a bottleneck. Here's where automation helps: Set a workflow trigger on new B2B contacts. When a new company is created in your CRM, send an automated WhatsApp message asking for their SST ID. Many CRMs support no-code automation rules that can send this immediately after contact creation. Create a required field for SST ID. In your CRM, make