Looks like Apple failed to update the recovery server images! Apples certificate expired!! Here’s more [https://appleinsider.com/articles/19/10/24/if-youve-got-an-old-macos-install-image-it-will-probably-stop-working-today|If you've got an old macOS install image, it will probably stop working today]
Here’s the needed image file [https://support.apple.com/en-us/HT208202|How to upgrade to macOS Sierra] Jump down to Step 4 for the download.