Any request without the header, from IAM Principals not in the bucket AWS account will be unauthorized with 403 Access Denied response.

So, yes all that is needed is to add the header to every request.

You can indeed support the request with a donation.

What helps even more is some help with research. I'd be particularly interested to know, if all that is needed, is to add the header to the request. No authorization is needed?

It looks like nobody else has voted for this.

Can I pay to have this implemented?

Thanks for your post.

I have added this request to the tracker:
Issue 2213 – Support for "Requester pays" S3 buckets
You can vote for it there.

I would like to access an Amazon S3 bucket which is not in my own AWS account, and has "Requester Pays" enabled. https://docs.aws.amazon.com/AmazonS3/latest/userguide/RequesterPaysBuckets.html

I would like to configure WinSCP to send the x-amz-request-payer request header with a checkbox labelled "Request Payer: Requester" to match the label used in awscli.

I can provide IAM access key and configured buckets for testing by DM.