How to use WhatsApp Business App and API with one number

Already using WhatsApp Business App to engage with customers? Want to upgrade to WhatsApp API for advanced features, but worried about losing everything you've built?

That's exactly what WhatsApp Coexistence is designed to solve.

Why businesses switch to WhatsApp API (and some don’t)

Before diving into Coexistence, it helps to understand what sets these two platforms apart and why businesses eventually need to scale up.

You've spent months building your business on the WhatsApp Business App. Your customer contacts, chat history, and relationships—everything lives in that familiar green icon.

Then you discover WhatsApp API, with its AI automation, team inbox, analytics, and ability to handle thousands of conversations at once. It's exactly what you need to scale.

But there's a catch: traditionally, upgrading meant choosing between two difficult options:

1. Delete your WhatsApp Business App account to migrate your number to the API—losing all your chat history, group conversations, voice/video calling capabilities, and the ability to ever use the Business App again on that number.

2. Get a new phone number for the API and keep your Business App—but now you're managing two separate numbers, confusing customers, and splitting your business identity.

For most businesses, it's tough to make the trade-off. Your chat history isn't just old messages—it's customer context, order details, and relationship history.

WhatsApp Coexistence changes everything.

Can you use WhatsApp Business App and API at the same time? Yes, with WhatsApp Coexistence.

WhatsApp Coexistence lets you onboard to WhatsApp API via an official WhatsApp Business Solution Partner (BSP), like SleekFlow, using your existing WhatsApp Business App account and phone number—no need to port your phone number, delete your WhatsApp Business App, and start over to accumulate contacts.

Once onboarded, you can engage with your customers using all the API features we mentioned above through SleekFlow's platform, while still keeping the ability to send 1:1 messages directly through your WhatsApp Business App whenever you need to.

Your messaging history stays synced between both devices, so you never lose context, no matter where you're responding from.

Your customers experience no disruption—they see the same trusted phone number. Your team gets the flexibility to scale operations without sacrificing the personal touch.

Benefits of using the WhatsApp Business App and API with one number

This feature was built specifically for small and medium-sized businesses that have started on the WhatsApp Business App and are now ready to scale their operations without disruption.

• For business owners: Get familiar with API features at your own pace, test what works for your team, and transition gradually—no pressure to switch overnight or risk losing your fallback option.

• For sales managers: Get complete visibility into your team's conversations in a centralized inbox without forcing them to change how they work.

• For sales & support agents: Keep using the familiar WhatsApp Business App for daily chats, while gaining access to powerful team features—collaborate with colleagues on complex cases, send bulk updates to your customer segment, and let AI handle routine questions so you can focus on high-value interactions.

Why is SleekFlow's WhatsApp Coexistence better?

While other platforms support WhatsApp Coexistence, here's what makes SleekFlow stand out:

1. Seamless import of your entire contact list and 6 months of chat history

While many WhatsApp API providers only sync new messages from the time of connection, SleekFlow automatically imports all contacts from your WhatsApp Business account and up to six months of your existing chat history, so your team has full context on the new platform from day one.

Contacts:

• All WhatsApp contacts with phone numbers

• Profile names and basic information

• Automatically deduplicated with existing SleekFlow contacts

Chat history:

• Up to 6 months of individual (1:1) conversations

• All message types (text, images, documents, voice notes)

• Chronological order preserved

• Message read/delivery status

• Media files and attachments

2. Assign contacts to your staff before they sync to the WhatsApp API inbox

Unlike other platforms that dump all contacts into an unassigned inbox, SleekFlow lets you assign contacts to team members right during onboarding—so your team has clear ownership from day one without the chaos of sorting through hundreds of unassigned conversations later.

3. Messages sent from the WhatsApp Business App trigger automations you've set up through the API

Unlike other BSP platforms, where messages sent through the WhatsApp Business App aren't linked to automations, SleekFlow ensures that any message—sent via WhatsApp Business App or API—can trigger workflows immediately.

For example, an outgoing message sent from the WhatsApp Business App can automatically:

• Update the customer's lifecycle stage and profile in SleekFlow

• Label and add a customer to a campaign list

• Update information on connected CRM platforms

This feature helps your operations stay efficient, wherever your team is working.

How to set up WhatsApp Coexistence for FREE?

We've always believed that businesses should be able to test the WhatsApp API without any upfront cost. With SleekFlow's free plan, you can get started with the WhatsApp API using your actual business number, all with zero commitment.

Setting up Coexistence takes just a few minutes:

1. Navigate to channels: In SleekFlow, go to Settings > Channels > WhatsApp

2. Select Coexistence: Choose "Connect your existing WhatsApp Business app via Co-existence"

3. Meta authentication: Log in with your Meta Business account through embedded signup.

4. QR code scan: Open the WhatsApp Business App and scan the QR code displayed.

5. Contact assignment: Assign new contacts to a person or team so they're easier to find and manage after import.

6. Background sync: SleekFlow automatically imports contacts and conversations while you continue working.

7. Auto top-up: Set an automatic top-up amount for the messaging fee so that it is added automatically via Stripe when the credit balance is low.

8. Complete: Your WhatsApp Business App remains active. SleekFlow is now connected.

Enable WhatsApp Coexistence now and keep using your WhatsApp Business App while gaining access to all of SleekFlow's powerful features. No migration headaches, no lost conversations.

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How does the message appear on the WhatsApp Business App & API after setting up WhatsApp Coexistence?

Once Coexistence is active, your conversations and contacts are perfectly mirrored in real-time between the WhatsApp Business App and your SleekFlow team inbox.

Any message sent or received in one place instantly appears on the other. When you reply directly from your WhatsApp Business App, the message appears in the SleekFlow inbox as "sent via WhatsApp Business App." This keeps your entire team aware of the conversation, preventing duplicate replies and ensuring every customer is handled promptly.

How does a 24-hour window work after setting up WhatsApp Coexistence?

Scenario 1: You need to message a customer first

When you need to start a new conversation, your choice of tool offers different advantages in cost and functionality.

Scenario 2: A customer messages you first

• When a customer initiates contact, it opens a 24-hour customer service window.

• Within this window, your team can send unlimited free-form messages (no templates needed) from either the SleekFlow inbox or the WhatsApp Business App.