A friend brought me DVD that plays fine on my computer, but when I try to play it on my Sony DVD player, I get a notice that this DVD is not recognized/playable in this device (or words to that effect).

The original DVD was made with iDVD.

What did my friend do wrong?

27" i7 iMac (10.13.6), iPhone Xs Max (12.1)

Those who can make you believe absurdities can make you commit atrocities. ~Voltaire