Let's say output.tf has the following. Notice in this example that "values" is used instead of "value". The correct key is "value", not "values".

output "example" {
  values = "hello world"
}

The terraform validate command can be used to know if you have any syntax errors.

]$ terraform validate
╷
│ Error: Missing required argument
│ 
│   on outputs.tf line 1, in output "example":
│    1: output "example" {
│ 
│ The argument "value" is required, but no definition was found.
╵
╷
│ Error: Unsupported argument
│ 
│   on outputs.tf line 2, in output "example":
│    2:   values = "hello world"
│ 
│ An argument named "values" is not expected here. Did you mean "value"?