S3 PutObject 403 permission denied errors

I have a bucket for which I am trying to upload objects into from a C# SDK application (.Net 4.6.1).

This is my public access block:

PublicAccessBlockConfiguration = new PublicAccessBlockConfiguration()
    {
        IgnorePublicAcls = false,
        RestrictPublicBuckets = false,
        BlockPublicPolicy = false,
        BlockPublicAcls = false
    }

The bucket has this policy applied to it:

{
    "Version": "2012-10-17",
    "Statement": [

        {
            "Effect":"Allow",
            "Principal": "*",
            "Action":[
            "s3:*"
            ],
            "Resource":[
                "arn:aws:s3:::testbucket2023/*",
                "arn:aws:s3:::testbucket2023"
            ]
        }
    ]
}

Calling code:

var request = new PutObjectRequest()
{
    BucketName = @"testbucket2023/testtag",
    Key = @"i/file.jpg",
    ContentType = contentType,
    InputStream = fileData,
    CannedACL = S3CannedACL.PublicRead
};
var response = S3Client.PutObject(request);

When I call PutObject, I get this error:

{"The request signature we calculated does not match the signature you provided. Check your key and signing method."}

Inner exception:

{"The remote server returned an error: (403) Forbidden."}

What else do I need to set to make this work? I will lock down the bucket to a specific principal once it is working.

This turned out to be a result of the AWS SDK being very out of date. Specifically, how they handle TLS has changed significantly. Simply upgrading to the latest fixed the error.