How do you get partnership with brands/businesses when you're not even started yet?

robruf

Let's pretend that a startup has a great and valid idea for a service. Thing is, in order to make this possibile, it needs to close parterships with other existing businesses. How do you get to those businesses and get those partnerships?

I'll use a real company as an example in order to explain myself better and try to avoid any misunderstanding:

let's take a company named Scalapay as an example. Scalapay is an italian startup who recently became the second ever italian unicorn. Their service allows people to buy stuff and pay in installments, with no interests at all. Even small amounts like 50 dollars can be divided into a few chunks and pay them monthly with no added interests.

Now, in order to offer their services, Scalapay had to reach out to ecommerces and make deals with them in order to be able to have their service listed as a payment option.

This is the part I am missing: how do you exactly reach out to big, estabilished brands/businesses when you're basically a nobody and get them to parter up with you?

I have an idea for a startup which I believe is really good, but in order to get started I would need to partner up with brands. How do you get to do something like that? Can investors help you with this as they surely would have a bigger and more valuable network then yours?