You cannot use the API (or at least certain entry points) without first verifying your account
If you fail to do this, your requests end with a 401 status.
Verify your account
There is no explicit option to verify your account. Instead, you need to import an existing mailing list. If you don't have a list to import, you can enforce this step by creating an artificial list, containing just your email. To do so, visit your Revue dashboard, Subscribers section, and click "Import from file":
.
Then, enter your email and two commas to skip your first and last name:

Submit and fill the next form.
When completed, a top ribbon indicates that the review is on its way:

You need to wait for the review to be completed.
Perform a request
To get your API key, visit your Revue dashboard, Account settings, Integrations, and scroll down to the bottom of the page:

Run something like:
const revueApiKey = "[your API key]";
const result = await fetch('https://www.getrevue.co/api/v2/subscribers', {
method: 'POST',
headers: {
Authorization: `Token ${revueApiKey}`,
'Content-Type': 'application/json'
},
body: JSON.stringify({ email: "john@example.com", double_opt_in: false })
});