"There is a message written in ballpoint pen in the magazine."

Translation: 잡지에 볼펜으로 쓴 메시지가 있다.

[KrKonar]

아이고 진짜

[Staffan431948]

Any reason for not accepting 있어요 instead of 있다?

[KungKras]

I would like to know this too

[KungKras]

Why 있다 and not 있어요?

[RQZ.Sash]

Why is it 쓴, not 쓰는?

[OlgaTheTerrible]

Past tense modifier. 쓰는 is being written. 쓴 has already been written.