Can inject operation but can't preapply operation, returns 400

Question

I can inject an operation but can't preapply an operation, it returns 400.

I checked the body's format and it's OK. Why does this rpc return 400? I can inject the operation.

Answer 1

The preapply/operations endpoint requires an array of operations to be submitted.

Just wrap your call around square brackets and it should work. This is how it's done in eztz.