Update SendGrid contacts with QB data

I currently use QB to store customer info. For example, John Doe is subscribed to A, Jane Smith is subscribed to B.  

We are looking to implement SendGrid to send marketing emails. For example: "check out our new subscription!"

I'd like to update contact in SendGrid from QB. For example, send "check out our new subscription!" to all customers subscribed to A. 

Does anyone have experience with this? I can manually upload a csv from QB to SendGrid, but I'm looking to automate this process. I don't have much experience with APIs, but would be willing to give it a shot if someone has been successful with this specific integration. 

Thanks!