Your registered agent must have a street address in the state that you are forming your business in. But every state has different regulations. For example, in Delaware, you are not required to declare an address for your business at all, but in Wyoming and Florida, it is a requirement. It can also be useful for the IRS.
But don’t worry. Generally speaking, any US address will do for most of the states. Some states don’t have even this restriction, but it is not recommended to use a non-US address just in case.
We can provide you with a Delaware address for only 99 USD/year, you can apply with this link.