You need to show more details... I cannot see what you are doing worng!

PM me if you want some help...


For what I am seeing you are trying BTC RBX pair!

1) Fill the "Price in BTC" you want.
2) Fill the "Amount of RBX" you want
3) Check if you have enouph waves for fee (0.003 WAVES)

Probably you dont have the WAVES...
It's a very small amount! Try some faucets and you get that easily.

https://wavesmine.com/jumpstart
http://www.wavesgo.com/
http://wavesplatformfaucet.com/
https://wavesdrop.com/