Time Machine: Files can’t be copied onto the backup disk because it is read-only

Hello, erahi.

Thank you for using Apple Support Communities.

From what I understand is that you're unable to use Time Machine because of a "read only" error. I'd like to help. You may not have to start over again. Have you had the chance to run Disk Utility to repair the disk? If not, check out this article: If you can't back up or restore your Mac using Time Machine

"Check your drives

• If you're using a drive connected to a port on your Mac or AirPort Extreme Base Station, make sure that the drive is turned on.
• If you're using a USB hub or a similar device, try connecting the drive directly to your Mac or base station.
• If you're backing up to an external third-party drive, check with the drive manufacturer to make sure the drive's firmware is up to date.
• If you're backing up to an external drive, check the formatting of the drive. Time Machine requires that an external drive be formatted like a Mac startup disk: Mac OS Extended (Journaled) with a GUID Partition Table (GPT). If you select a differently formatted drive for use with Time Machine, your Mac automatically prompts you to erase it for Time Machine.
• Reformatting a disk erases all data stored on the disk, so you might want to move important files to another disk first.

If your drive is already formatted correctly, turn off Time Machine, then check it for problems:

• To check the drive of an AirPort Time Capsule, follow the steps to verify an AirPort Time Capsule drive.
• To check an external drive connected to your Mac, open Disk Utility from the Utilities folder of your Applications folder. Then use the First Aid feature in Disk Utility to verify your disk. Do this for your startup disk as well".

Keep me updated.

Hello, erahi.

We're glad to hear everything has been resolved. Reach out to Apple Support Communities if you need help with anything else.

Cheers!