Scheduled maintenance and system updates do not negate the existence of the service. This is why Support recommends to try again later, or to submit a Standard RMA as an alternative. Additionally, warranty-specific considerations can delay the process. For example, if you are in the US and your hard drives come from the EU you’ll need to amend your warranty before an ADV RMA can be submitted. You can still process a Standard RMA on such cases since it’s worldwide warranty.
Many users misunderstand a specific instruction as an error. The following thread is an example: