You will need to have an account with Flowroute.
There are setup fees associated with purchasing a DID, oftentimes very minimal. You will need to have available credit in your account to cover any setup fees. To add credit to your account, see the steps in this article.

Log in to your account at Flowroute Manage Portal.
Click DIDS, and then go to the Purchase tab.
To make a search easier, use Filters on the left side. Additionally, you can sort results using different criteria. Once you set up desired filters click Apply Filter to see updated search results.
To purchase a number simply click the Purchase button next to the DID number
Next thing, you'll see a pop-up message asking you to provision messaging services on a selected DID number - select Yes if you're going to use this DID number for SMS/MMS services. Select No if you're only planning to use this DID number for voice services. If you change your mind, you can always adjust this setting from the DIDS menu.

You shall see a notification about successful purchase in the top right corner of the page:

You can access all DIDs you purchased (and/or ported into your Flowroute account) in the DIDS → Manage section.

For bulk DID purchases, we highly recommend you use our Numbers API.

Which states or countries can I purchase DIDs in?