A "-2003" error while booting into Internet Recovery Mode indicates a networking issue of some sort. Connect the Mac directly to the router using an Ethernet cable including any necessary adapter(s) for a faster more reliable network connection which also bypasses any hard to troubleshoot WiFi issues.
If you have access to another Mac you can create a bootable macOS USB installer using the instructions in this Apple article:
How to create a bootable installer for macOS - Apple Support
The other Mac needs to be compatible with the OS you want to download as mentioned in the Apple article.
Here is an Apple article with the steps you should perform when selling or giving away a Mac:
What to do before you sell, give away, or trade in your Mac - Apple Support