We are currently integreated with Basecamp 2. We hope to integrate with Basecamp 3 in the future, but at the moment Basecamp 3 doesn't offer an API to integrate with (see this page on their site)
To integrate your Proposify account with your Basecamp 2 account, go to your account settings and click on the Basecamp icon
Enter your account ID (in the URL when you're logged into Basecamp)
Allow Proposify to access Basecamp
After you connect your Basecamp account you'll be able to import contacts from Basecamp into Proposify.
After your proposal has been accepted by one of your clients, you can automatically create it as a project in Basecamp and upload a PDF of the proposal to your file section. You can also invite teammates and your client into the Basecamp project.
To do this, first go to the Proposal Snapshot page of your Won proposal, and find the Base button near the top of the page. Then you'll be prompted to create the project, which will automatically be entered into Basecamp.