Using redirects to point to /.netlify/images/ results in "must provide the url param"

I’m having a curious issue, because it works perfectly with netlify dev so the config should be correct, but it fails on any deployed sites.

I am trying to use the image cdn to access images stored on another storage service I control.

I would like to avoid using /.netlify/images/ in my URL, so I set up a redirect in my netlify.toml:

[[redirects]] from = “/image_cdn/*” to = “/.netlify/images/:splat” status = 200 force = true 

When viewing a URL locally using netlify dev the image is returned, resized as requested:

if I change the root domain in the URL to our production site, without changing any of the params:
{"code":400,"msg":"must provide the url param","error_id":"01K9PVPFHJRP582AKGZVW2JJXS"}

I deployed the changes to netlify.toml on main / my production site, because I know the netlify.toml config is site-wide, including deploy previews.

I can’t figure out what I’m doing wrong, I’ve read and re-read the docs many times, as well as searched on the forum. Given that I’m hosting the files on an external URL, I have no reason to suspect redirect loops or context-specific deployment problems.

Help welcome! Thanks!