I have to send messages to the customer's whatsapp number programatically.
What are the pre requirements/needs?
Do I need to convert/register my personal number to business account?
Is there any API provided by whatsapp for this?
Do I need to convert/register my personal number to business account?
Not necessarily, it's your choice if you want to share your personal account, even though you recommend using a business account
Is there any API provided by whatsapp for this?
According to Whatsapp's own documentation, they do not have a direct API, but you can create a link to send the messages, according to the documentation, follow the submission parameter by the URL: https://api.whatsapp.com/send?phone=
Here's another example:
Use: https://api.whatsapp.com/send?phone=15551234567
Don't use: https://api.whatsapp.com/send?phone=+001-(555)1234567
You can see more in: https://faq.whatsapp.com/en/android/26000030/