data preprocessing: empty 'tgt' text

[connie-n]

Hi,
I'm doing data preprocessing with my own data.
I converted my data to json file which has 'src', and 'tgt' dictionary.
and then run data preparation code step 2, 3, 4, 5.

but there is no tgt text. It's empty. all text is input as 'src'.
could anyone help me?

my data shape is below.

below is the data shape which is done step3&step 4.
all tokenized word is put as 'src'....

[connie-n]

I added '@highlight' before summary sentence and it was cleared. thanks.