What do I do if my card say bad card. Try to redeem it and it said that the card was bad

Follow there instructions provided in the link below.

If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support

My friend of my bought an Apple Gift Card from Australia and send it to me and I try to redeem it and it said is a bad card. What should I do next

Gift cards can only be used in the country or region it was purchased in. Are you in Australia?