What are the tax responsibilities for an Indian author in Sri Lanka?

If a book of Hindi stories is edited and published in Sri Lanka, what responsibilities does the Indian author have? What is the income tax percentage? And is GST applicable? If yes, will the royalty received in the author's personal savings account lead to any dispute? When I spoke to a CA, they said GST is applicable, for which the firm must be registered. They mentioned that if the firm is not closed, I will receive notices every three months. What does this mean? And how can I handle it? If the publisher in their country pays taxes, how will taxation apply to the author's royalty in India? Please provide guidance from an experienced legal professional.