I deleted the os from my mac mini and I can’t reinstall another one…

A 2014 Mac mini.can run up to macOS Monterey.

Your not the first to report trouble reinstalling Sierra.

Try Option-Command-R during startup and see if you can install the latest macOS version available for that model.

see > How to reinstall macOS - Apple Support

I'm sorry to hear about your installation issues. This is a somewhat common problem, and there are several potential solutions that you can try. Here's a list of steps that might help resolve your issue:

1. Check your Mac's date and time settings: Sometimes, this error can occur if the date and time on your Mac are incorrect. Boot your Mac into recovery mode (press Command + R when starting your Mac). In the menu bar, choose "Utilities" and then "Terminal". In the terminal, type `date` to check the current date and time. If it's incorrect, you can set it to the correct one by typing `date -u {month}{day}{hour}{minute}{year}`. For example, if today is July 29, 2023, at 12:34, you would type `date -u 072912342023`.

2. **Ensure you have a stable internet connection:** Internet recovery requires a reliable internet connection. Make sure you're connected to a stable network, preferably via an Ethernet cable for the best stability. If you're using Wi-Fi, try to be as close as possible to the router to have the best signal.

3. Reset NVRAM and SMC: Try resetting the NVRAM and SMC on your Mac. To reset the NVRAM, restart your Mac, then immediately hold down the "Option + Command + P + R" keys for about 20 seconds. To reset the SMC on your Mac mini, shut down your Mac and unplug the power cord. Wait 15 seconds, then plug the power cord back in. Wait another 5 seconds, then turn your Mac on again.

4. Use a bootable installer: If the above steps don't work, you can try creating a bootable installer for macOS Sierra on a USB stick or other external drive. This way, you can install macOS Sierra without relying on Internet Recovery. Apple provides instructions for creating a bootable installer.

If none of these options works, it might be worth taking your Mac to an Apple Store or an Apple Authorized Service Provider for further assistance. They can help you troubleshoot any potentially more complex hardware or software issues that may be preventing the installation from proceeding.

What exactly are you trying to accomplish by reinstalling Sierra instead of a later macOS version?

If the Mac mini was running macOS High Sierra or later, then you will need to erase and reformat the drive from APFS back to Mac OS Extended Journaled before you can reinstall Sierra.