GST for Print on Demand Business in India and Abroad

Hello All, I have recently started print on demand business for t-shirts in India and planning same for USA, and Canada. Process Followed For India 1: I am planning to sell through Website to Indian audience within India except few states in North. I shall add designs printed on t shirt and sell it through website 2: When someone orders, t shirt online, it would be passed to vendor who would print my design on their t-shirt and ship it to client and in due process vendor charges me with costing and gst, however I have not charged my client GST 3: My vendor is based in Chennai and they do charge me for GST for every sell. I would like to know is GST needed for this business model as there are several discrepancy that say not needed untill some xx amount sale is done and some mention its needed from beginning? Also is it mandatory to charge GST to your customers in India for this model or not? Process Followed in USA and Canada Process of selling is same with difference that my vendor now is based in USA and Canada, and they would print and ship it clients. Do I need GST for this model with perspective that I woudl file my returns here for my business in India.