WhatsApp Business for accountancy firms: a practical setup guide

Most UK firms have at least one partner already messaging clients on WhatsApp from a personal number. The question isn’t whether clients want to use it — clearly they do — it’s whether the firm can adopt it deliberately, without breaching ICAEW client-money and confidentiality expectations, UK GDPR, or its own PI cover. This guide walks through the two products called “WhatsApp Business,” what each one actually gives you, and the practical and regulatory checks before you go live.

There are two products, and the difference matters

Meta sells WhatsApp to businesses through two distinct channels. They share branding but almost nothing else.

• WhatsApp Business app — a free mobile app for a single business phone number, intended for sole-traders and very small businesses. One device, one phone number, manual replies, optional “quick replies” and a basic catalogue. It can be linked to up to four extra companion devices (WhatsApp Web, desktop), but everything still flows through one number and one primary handset.
• WhatsApp Business Platform — the API, usually consumed via Meta’s Cloud API or through a Business Solution Provider (BSP) like Twilio, MessageBird, or 360dialog. Multi-agent inbox, integration with your CRM/practice management, template messages, automation, webhooks, and proper auditability. This is the product any firm with more than one or two practitioners actually needs.

Conflating the two is the most common mistake we see. The free app is a personal tool with a business skin. The Platform is an enterprise messaging product with conversation pricing, a verified business profile, and a paper trail.

What the free app gives you

For a sole practitioner with a handful of clients, the free WhatsApp Business app is genuinely useful. You get a business profile (opening hours, address, website), labels for organising chats, away messages, and quick replies for things like “please send your latest mortgage statement.” You can export chat history per conversation. It’s fine for a single principal who is the only person ever replying.

It is not fine the moment two staff need access to the same client conversation, or you want chats to be retained centrally rather than on a personal device, or you want to integrate the channel with your practice management system. You will hit those limits within a few months of taking it seriously.

What the Platform (API) gives you

The Business Platform is what powers every credible firm-wide WhatsApp deployment. The features that matter for an accountancy practice:

• Multi-agent inbox. Several reviewers can handle messages for the same client; the conversation is owned by the firm, not by an individual’s phone.
• Verified business profile. The green tick. Required to reassure clients the number is genuinely yours and not a scam.
• Template messages. Pre-approved messages you can send outside the 24-hour customer-service window (e.g. “Your quarterly update window is now open — please send June bank statements”). Templates must be approved by Meta in advance.
• Webhooks and automation. Inbound messages and media post to your own backend, so you can route, categorise, or trigger downstream work.
• Central retention. All message history sits on the API platform and your downstream systems, not on a partner’s phone.

How conversation pricing actually works

Meta does not charge per message. It charges per conversation, a 24-hour window opened by the first qualifying message between the firm and the client. As of the 2025 rate card, four conversation categories apply, each priced separately by country. For the United Kingdom:

• Service conversations — initiated by the client (or by you within the existing 24-hour service window). Free from 1 November 2024, after Meta dropped the per-conversation charge on inbound service traffic.
• Utility conversations — firm-initiated, for transactional updates (“your return is ready to sign,” “quarterly window now open”). Roughly £0.025 – £0.04 per conversation in the UK, depending on the BSP’s margin on top of Meta’s wholesale rate.
• Authentication conversations — for OTPs and login flows. Similar UK price point, around £0.025. Rarely relevant for an accountancy firm.
• Marketing conversations — promotional outreach. UK pricing is materially higher (around £0.05 – £0.08) and you almost certainly should not use this category for client communications. A firm that markets to clients on WhatsApp will fail an ICAEW conduct check very quickly.

BSP per-message fees may apply on top of conversation pricing — Twilio, for example, adds a few tenths of a penny per inbound or outbound message. For a firm doing real volume, model both.

Worked example: a 200-client firm, MTD ITSA quarter

Take a mid-sized firm with 200 landlord clients on MTD ITSA, each receiving one quarterly nudge from the firm (“please send Q2 bank statements and any property expenses”) and replying with three or four messages over the next few days.

• 200 utility conversations at £0.03 each = £6.00 per quarter on Meta’s conversation fees.
• ~800 inbound and 800 outbound messages within the resulting service windows. At a typical BSP rate of £0.004 each, that’s £6.40 per quarter.
• Total channel cost ≈ £12.40 per quarter — about £50 a year across 200 clients, or 25p per client per year.

Even doubling those assumptions, the channel itself is rounding error against the time saved chasing documents. Where firms burn money on WhatsApp is invariably people-cost (manual replies, no routing, no audit trail), not Meta’s per-conversation fee.

Client consent and ICAEW expectations

ICAEW’s Code of Ethics and the firm-wide AML requirements don’t prohibit WhatsApp, but they do require firms to keep client communications confidential, retrievable, and auditable. A few practical points firms get wrong:

• Get explicit, recorded consent. The engagement letter or a separate channel-consent form should set out that WhatsApp will be used, what it will be used for (document collection, status updates), and that messages are processed and retained by the firm and its subprocessors. Don’t rely on the client just messaging you first as implied consent.
• Don’t use personal phones for client chat. A partner’s personal handset is not a firm record. If they leave, the chat history leaves too — and the firm has lost client communications it had a duty to retain. The Business Platform plus a central inbox avoids this entirely.
• No tax advice on WhatsApp without a written follow-up. Treat WhatsApp as a collection and status channel. Substantive advice goes in writing through your normal advice channel, with the WhatsApp exchange referenced. This protects PI cover.
• Don’t share other clients’ data. Forwarded screenshots, group chats including multiple unrelated clients, and casual photos of office screens are confidentiality breaches.

UK GDPR considerations

WhatsApp is operated in the UK by WhatsApp Ireland Limited, with onward processing by Meta Platforms Inc. in the United States. The ICO has historically taken the position that using WhatsApp is lawful provided you do the work: a documented lawful basis, a Data Processing Agreement (DPA), an international data transfer mechanism (UK Addendum to the EU SCCs in practice), and a clear retention policy.

For an accountancy firm, the realistic position is:

• Lawful basis — contract (performance of the engagement) for most operational messages, with legitimate interests as a fallback for status updates. Marketing on WhatsApp needs separate consent and is generally inadvisable.
• Update your privacy notice to list Meta / WhatsApp Ireland and your BSP as processors, with the categories of data and retention period.
• Retention — align WhatsApp records with your normal client-record retention (six years after end of engagement is the usual benchmark; check your firm policy). The Business Platform exports cleanly; the free app does not.
• Subject access requests — you need to be able to find a specific client’s messages in response to a DSAR. If your only copy lives on a partner’s personal phone, you can’t answer that request reliably.

Practical setup checklist

1. Decide product. If you have more than one client-facing staff member, skip the free app and go straight to the Business Platform via a BSP.
2. Verify the business. Get a Meta Business Manager account, complete business verification, and apply for the green tick. Allow two to four weeks; Meta is slow.
3. Get a dedicated number. A new VoIP or mobile number that has never been used on personal WhatsApp. Don’t port a partner’s number.
4. Approve template messages. For each firm-initiated message you’ll send (quarterly nudge, document-missing reminder, return-ready-to-sign), submit templates to Meta in advance.
5. Wire up retention. Webhook the inbound traffic into your practice management or document store, so the message and any attached files end up in the client record automatically.
6. Update your engagement letter, privacy notice, and AML risk assessment to reflect WhatsApp as a channel and Meta / your BSP as processors.
7. Train staff. No tax advice without written follow-up. No personal phones. No screenshots of other clients.

The Otto build, briefly

Otto is built on the WhatsApp Business Platform via Twilio, which is the same stack we describe above. We chose it for the same reasons a firm would: multi-agent, central retention, template approval, and webhook-driven automation. The client never installs anything — they message a number — and the reviewer at the firm sees a structured intake in the Otto portal rather than a thread on a phone. Onboarding clients to the channel is covered separately in our landlord onboarding guide.