Hola!, 1st timer needs a little help.

Hola Amigos, My name is Diego and it's my first time growing indor.
I got some clones that are OK sofar, but I have a 10 day little plant from seed that it was going great untill started showing some brown spots.
I will post a picture of it so you can see.
I am using soil and since I'm from Argentina we use YERBA MATE in soil for plants so it has a part of that on the soil.

At first I was not spraying with water but I started yesterday to do but is not better.

Any Ideas?

Thank you.

Only water when the soil is dry.
What kind of lights?

yeah its hard to tell without more info