If you go here: http://rest.s3for.me/check/

Why is your key id called 'AWSAccessKeyId', why does your error message say 'AWS Access Key Id does not exist in our records' why is your error message identical to the letter of what S3 would return. Surely the error message text isn't required for protocol validation.

This looks like you just took an open source S3 REST API clone (there are many) and stuck it on a Hetzner server without bothering to change any variable names.

To me there are a lot of questions, the most obvious tell is that I highly doubt Salesforce would use a stock image as the logo for their cloud database solution considering the level of investment they made in it.