Op command does not exist

I am a person obsessed with custom items and blocks. Recently, I made a suspicious sand that contains a comand block, and it has the command: "op @a[distance=..30]". When I was done, I put it in a command block. When I checked the command, it said that the op command did not exist. I've created this world about a month ago, and I turned my cheats on and it's singleplayer. However, the issue still persists. I attached the command in a text file.