Why isn't my /execute command working?

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I put in this command through Bedrock:
/execute @a ~ ~ ~ detect ~ ~-1 ~ sand 1 effect @p instant_damage 1 15
Although when I go to use it, it says:
Syntax Error: Unexpected "remove": at "t ~ ~-1 ~ >>remove<< @p'
Please help, thanks.
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How does execute command work in Minecraft?
/execute executes another command but allows changing the executor, changing the position and angle it is executed at, adding preconditions, and storing its result.Why do my command blocks not work?
Due to the power of the command blocks, there are a few conditions that need to be met in order to use them in your server. First, you will need to enable command blocks directly in the server settings. Secondly, you will need to be OP on the server and in creative mode to be able to place the block.How do you execute a command block?
Steps to Use a Command BlockWhy Isn't It Possible
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