Create a Spotify Application
Put aside:
Client ID
Client Secret

Click on Edit Settings
In Redirect URIs:
Add 

Refresh Token
Navigate to the following URL:
https://accounts.spotify.com/authorize?client_id=SPOTIFY_CLIENT_ID&response_type=code&scope=user-read-currently-playing,user-read-recently-played&redirect_uri=http://localhost/callback/
After logging in, save the CODE portion of: http://localhost/callback/?code=CODE

Create a string combining SPOTIFY_CLIENT_ID:SPOTIFY_CLIENT_SECRET (e.g. 5n7o4v5a3t7o5r2e3m1:5a8n7d3r4e2w5n8o2v3a7c5) and encode into Base64.

Then run a curl command in the form of:

curl -X POST -H "Content-Type: application/x-www-form-urlencoded" -H "Authorization: Basic BASE64_HERE" -d "grant_type=authorization_code&redirect_uri=http://localhost/callback/&code=CODE_HERE" https://accounts.spotify.com/api/token
Save the Refresh token
Vercel
Fork This Repo

Register on Vercel (Log in with GitHub)

Create project linked to your GitHub repo

Add Environment Variables:

https://vercel.com/<YourName>/<ProjectName>/settings/environment-variables
SPOTIFY_REFRESH_TOKEN
SPOTIFY_CLIENT_ID
SPOTIFY_SECRET_ID
Deploy!

Add to Your Readme
### Spotify Playing 🎧

[<img src="https://<YOUR VERCEL SERVER URL>/api/spotify-playing" alt="Spotify Now Playing" width="350" />](