I imagine that all your Shopify products already have a UPC or EAN barcode, right? Do you already have the images as requested by Amazon? Do you have the necessary information to build the Listing, such as Title, Description, Keywords? I recommend that you do not leave this task to people from India or Pakistan, they will do a horrible job for you.
My name is Nicolás, I have been working with Amazon for 4 years.
I specialize in Listing Optimization with SEO Positioning, Study of Keywords and development of PPC Campaigns.
I have worked with brands from the USA, Canada, the United Kingdom, Spain, Mexico, Argentina and Greece.
I use tools like Jungle Scout, Helium10, Keepa and Excel
Hope to hear from you soon.
Regards, Nico