I've cleaned off old iMac for trade in but am unable to reinstall macOS is that OK?

What is preventing you from reinstalling the OS?

You should attempt to reinstall the macOS. Don't worry about installing any updates or upgrades afterward. Use Shift-Option-Command-R or Option-Command-R at reboot to initiate the recovery mode. Then select Reinstall macOS when the machine presents the Utilities window.

How to reinstall macOS - Apple Support

I successfully walked through the steps to set my 2016 Macbook to factory mode, until this point. I attempted 3 times to reinstall MacOS Sierra, but it shows the same error on the initial post. Is there something else I can do?

If it doesn't work, and I send it in for trade-in, will that interfere with receiving the trade-in value?

Yes, a Mac that doesn't match the functioning condition that was claimed may affect the trade in value.

What error do you encounter when you try to reinstall the macOS Sierra?

Can you successfully boot the Mac to recovery mode and to the macOS Utilities screen?

Select "Macintosh HD" and continue to completion.

If that fails, click Quit Reinstall macOS. Do not restart the Mac, you need to remain in the Recovery mode for the next bit.

From the macOS Utilities screen, select Disk Utility. Then click View > Show All Devices and select the topmost internal device (not an indented volume). Click the Partition button in the toolbar. Set the Name: to "Macintosh HD", select Mac OS Extended (Journaled) as the format and use the GUID partition scheme. Click Erase and wait for Disk Utility to report the task done. Quit Disk Utility and return to the macOS Utilities screen.

Select Reinstall macOS Sierra again and attempt the reinstall one more time, selecting Macintosh HD as the destination drive.

In the menu bar, you'll have to click the app name - Reinstall macOS - and then click Quit.

I see the error message. Unfortunately it's pretty non-specific.

You can run Disk Utility again, this time select the Macintosh HD volume and run First Aid. Run it until it ends with no errors. Then run First Aid on the drive device itself, the topmost internal device. Again, run it until it ends with no errors.

When done with Disk Utility > First Aid, attempt to reinstall macOS a final time.

If you run First Aid more than a few times on the volume or drive and still it returns an error and can't fix problems that it might find, then I suggest the drive is failing and you've done all you can do. You'll just have to return the Mac as it is and hope for the best.

When the Mac is received, it will be evaluated and the trade-in value may (or may not) be adjusted. If it is adjusted, you will be emailed with the info and given an opportunity to accept or decline the revised trade-in value.

I had a similar issue so I just returned it and no issue. They run a diag. test anyway and wipe the system so not sure it matters much.

Ok, I attached a picture of the error. I don’t see an option to click “Quit Reinstall macOS”.