Getting 501 Not Implemented trying to list multipart uploads

I’m using the Soto library to do a multipart upload to Spaces. I seem to get “501 Not Implemented” responses when trying to make a simple ListMultipartUploads request

At least, I think that’s what’s going on. The Soto library hides a lot of the complexity, and relies on Swift NIO, which is designed for extreme performance, and is thus very async and very hard to debug. The request has this content (forgive the excessive formatting):

p preparedRequest.url
(Foundation.URL) "https://<redacted>.sfo2.digitaloceanspaces.com/?uploads="

p preparedRequest.head
(NIOHTTP1.HTTPRequestHead) {
  _storage = 0x0000600002102fc0 {
    method = GET
    uri = "/?uploads="
    version = (_minor = 1, _major = 1)
  }
  headers = {
    headers = 5 values {
      [0] = (0 = "user-agent", 1 = "Soto/6.0")
      [1] = (0 = "host", 1 = "<redacted>.sfo2.digitaloceanspaces.com")
      [2] = (0 = "x-amz-date", 1 = "20240731T062806Z")
      [3] = (0 = "x-amz-content-sha256", 1 = "e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855")
      [4] = (0 = "authorization", 1 = "AWS4-HMAC-SHA256 Credential=<redacted>/20240731//s3/aws4_request,SignedHeaders=host;x-amz-content-sha256;x-amz-date,Signature=<redacted>")
    }
    keepAliveState = unknown
  }
}

Body:
<?xml version="1.0" encoding="UTF-8"?><Error><Code>NotImplemented</Code><Message></Message><RequestId>tx000002f996400c083ddc3-0066a9e215-b9ef07e-sfo2b</RequestId><HostId>b9ef07e-sfo2b-sfo2-zg02</HostId></Error>

I am not including x-amz-expected-bucket-owner in the request, I’m not sure what to put there, or why it’s even needed, since I have credentials for the bucket.