Error 502 after installing Lets Encrypt on Digital Ocean VPS

Those settings look good at the Cloudflare end.

After installing Certbot, did you successfully install a Let’s Encrypt certificate?

Which Crypto->SSL setting are you using? Full, Full/Strict, or Flexible?

Which 502 error are you getting? Top or bottom, according to the following support article:
https://support.cloudflare.com/hc/en-us/articles/218378978-What-should-I-do-after-seeing-a-502-or-504-gateway-error-on-my-site-