Can't upload to S3 (Cloudflare R2)

I was setting up R2 on my site following some guides here but no I just see a generic Sorry, but your upload failed. Please try again. message when I try to upload a file. The only thing I see in the logs are this:

I have my URLs configured in the app.yml file because the web UI was rejecting my URLs as structured in the how-to posts (invalid format):

image
The CDN_URL is the custom domain (as set in Cloudflare) and the S3_ENDPOINT is the URL in the web panel. I have all of my options configured properly with correctly created auth tokens:

It looks like Cloudflare is seeing some requests but nothing is being stored.

What is the problem?

Hey,

Is it not because of the final slashs (/) in the s3 cdn url and the s3 endpoint?