Hello nagalavanya!

Thanks for reaching out to us. Let me assist you in sending customer statements.

Currently, we're unable to send customer statements via WhatsApp. You can only send them by email.
Also, we can't attach the statement to the invoices. They must be sent separately.

Please check this article on how to create and send a statement in QuickBooks Online: Create and send customer statements in QuickBooks Online. This includes steps on how to customise it.

Post again here if you need more help. Take care!