Setup Requirements:
Full Control Admin or Owner of Business Portfolio on Meta Business.
The Business Portfolio is with no restrictions.
Tips - To check your Account Overview, go to Business Support Home and select the right Business Portfolio to view.
Turn off 2FA in WhatsApp Manager.
Step-by-step Guide
Logon to iSlash AI Platform at https://app.islash.io/
Go to Settings:

Go to Channels and Click on "+" to create a new channel.
Under New Channel,
Name : rename the channel, we recommend keeping it simple to just "WhatsApp API"
Timezone : update timezone according to your location.
Platform *important : select "WhatsApp Official API (iSlash)"
Migration Channel : tick to enable.

Click Save and then click on "Continue with Facebook":

An external window by Meta will pop up. You will either be required to log in to your Facebook account, or simply click “Continue as [Your Facebook Name]”.
Grant permission to iSlash AI Platform by clicking “Get Started”.

Select the Business portfolio with WhatsApp Business Account to migrate and click "Next".
Choose "Create a new WhatsApp Business Account" and "Create a new WhatsApp Business profile", click "Next" to proceed.
Enter the WABA details, then click "Next" to proceed.
WhatsApp Business Account Name: Please ensure it's consistent with the WABA name in your WhatsApp Manager Overview section.
WhatsApp Business Display Name: Please ensure it's consistent with the Display name in your WhatsApp Manager Profile section.
Category: Please ensure it's consistent with the setting in your WhatsApp Manager.
In the next section, select "Add a new number", fill in the number to migrate.
Choose either text message or phone call for verification, then click "Next".
You'll be prompted about an existing WABA on this number, if you continue, your number will be moved to your new WABA in 1Slash Limited.
Click "Next" again.
Complete your Business Portfolio by entering the verification code and click "Next".

On the next page, click "Continue" and then "Finish" to complete the part at Facebook popup.
Wait a moment while system is configuring your account, system will show "Success" when it's completed.
Back at iSlash AI platform, click "Start Migration".
At the confirmation popup message, click "Confirm".
Test message: Please proceed to send message to this number and reply to it.
Sync Message Template
Only high quality message templates from a blue tick verified WABA will be migrated.
Go to Settings.
At the left panel, select "Message Templates".
At the top right corner, click "Sync".
Your high quality message templates will then be synced.
FAQ
Can I find the chat history from previous WhatsApp API platform?
No, chat history won't be migrated from previous platform.
There's error when I click "Start Migration" (step 14), what should I do?
If there is error, at Channel, scroll down to Action section, click "Register"; then try again.