Airport Time Capsule error -6.727

It does, thank you.

I went over my notes on TC-related error codes, but I could not find anything specifically on the code (-6.727) that you are seeing.

The only ones "close" would be the following, and what they would indicate:

• Error 6584: It points to a problem with your Mac's filesystem. Use Disk Utility to repair your Mac's disk, and then attempt the backup again.
• Error 6736: This error might occur if the Time Capsule's firmware is outdated. Update the Time Capsule's firmware through the AirPort Utility.

Obviously, since you were able to update the firmware, the second one would not be relevant.

... so this will require a bit more troubleshooting, which you may or may not want to go through the trouble to do so, since it will require looking at macOS log entries that were created during a backup process. Something you may want to do before digging deeper, is to boot up your Mac in Recovery Mode, and then, run the Disk Utility to check for any errors on your Mac's system drive.

One excellent tool for this is called Mints. It's a free troubleshooting app from the Eclectic Light Company. With it, you can review the log entries for the last failed TM backup to potentially discover what is going wrong.

The following article should help explain what a "good' backup would look like, using Mints, and provide you with a link on downloading a copy.

• Time Machine 16: Reading a normal backup in Catalina using Mints - The Eclectic Light Company

Let's start with: Which exact model is your Time Capsule?

When do you see this error:

• When trying to update the TC's firmware?
• When performing a backup?

Ok, thanks for the additional information. The latest version of firmware for this Time Capsule (TC) model is: 7.9.1.

FYI, Apple has not released any newer firmware for any of their AirPort base station in quite some time since they decided to exit the networking hardware business back in early 2018.

Regardless, if you are getting this error when attempting to update, we would need to know a bit more about your current network configuration that you are using this TC with.

For example:

• Is this TC your "main" Internet router? That is, is it connected directly to an Internet modem, and NOT to another router/gateway upstream of it?
• Did you purchase this TC new and have been upgrading its firmware all along, but ran into this issue just recently when trying to update it?
• Or, did you purchase this TC used and had this issue from the get go?

About your iMac:

• Which exact model is it?
• What version of macOS is it currently running?