What does the error message mean, with an exclamation point in a traingle, labelled "apple.com/support -1007F"

Does this cover the problem? For more extensive information see About macOS Recovery.

If you can't start up from macOS Recovery

If your Mac can't start up from its built-in macOS Recovery system, it might try to start up from macOS Recovery over the Internet. When that happens, you see a spinning globe instead of an Apple logo during startup: 

To manually start up from Internet Recovery, press and hold either of these key combinations at startup:

• Option-Command-R
• Shift-Option-Command-R
• Learn more

If startup from Internet Recovery is unsuccessful, you see a globe with an alert symbol (exclamation point):

In that case, try these solutions:

• Make sure that your Mac can connect to the Internet. If you're not prompted to choose a Wi-Fi network during startup, move your pointer to the top of the screen, then choose a network from the Wi-Fi menu , if available.
• Press Command-R at startup to try using the built-in Recovery system instead of Internet Recovery.
• Connect to the Internet using Ethernet instead of Wi-Fi, or vice versa.
• Connect to the Internet from a different Wi-Fi or Ethernet network. Your network configuration might not allow the Internet access that macOS Recovery needs.
• Try again later, because the issue might be temporary.
• Start up from another disk or volume, if available, or use a bootable installer to reinstall macOS.

If you still need help, please contact Apple Support.