Make sure your Trusted Root CA is the one installed on your Web Server(s).

You are correct. When connectivity to your circuit was originally set up, you needed to complete an REF. At that time, Fund Transfers was not an application that was being implemented for your connectivity profile.

A DNS URL contains a name, whereas a non-DNS URL contains an IP Address.

Make sure your Web Service is up and running. Make sure we have the updated URL on file.

No. You can go directly into Production.

DTCC does not validate/compare the Attachment(s) in the message with the MimeTypeTC since DTCC does not open the attachment(s).  The Sender and the Receiver should be able to validate this.  Note: The Receiver can always reject the message if they perform mime type validations against the actual attachment type in the message.