Payment

[GinaP1]

Hello:

I have a shopify store and ship only using Media Mail (books).  I want to add products to my online store, but now I have to add First Class shipping and International Priority.   How can I change my shipping preferences so customers can add products to their Media Mail shipping without first checking out and going back to the store to purchase products that are not media mail?  

thank you in advance for any help and response.