I think "This is an order from mother, so you have to do it" sounds like more natural English.
Any specific reason this is not accepted? "This order is from mother, so you have to do that."
That would be "Perintah ini dari ibu..." - ini modifies the noun only when it comes after it.
It's an easy mistake to make, but the course likes to be very picky about this, so it's good to note this behaviour.
Thanks - makes sense.
should this order is from mother so you have to do it be accepted