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Choose the Git Repository (GitHub, Bitbucket, or GitLab) where your app is located. An authentication popup will appear, letting you select the account or organization to grant access. You don't need to provide access to all your repositories, but you can adjust permissions later in GitHub/Bitbucket/GitLab to add more repositories.
After linking your git provider, you'll move to the second step automatically. Select your account from the git provider, then choose the repository containing the Meteor app you wish to deploy.
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Now, simply click on "Next Step" to reach the third and final step.