Failure while generating tidal constituents

[jphastings]

I've been tying to use this site (specifically https://neaps.js.org/harmonics/) to generate tidal constituents (with data adapted from Tower bridge tides @ https://tidepredictions.pla.co.uk/), but I'm receiving this error in my dev console:

Uncaught (in promise) TypeError: Cannot convert undefined or null to object
    at Function.keys (<anonymous>)
    at companion-bubble.js:1452:20487
    at Generator.next (<anonymous>)
    at An (companion-bubble.js:1452:19905)
enigmatic-sea-16360.herokuapp.com/api/v1/:1          Failed to load resource: the server responded with a status of 404 (Not Found)

Could this be connected to Heroku's removal of its free tier?