Cannot embed code js with token

Hello everyone,

I am a bit confused in adding an embed code of js with token that would be added inside a doctype through html type document.

The code is as follow:

<script src="" defer></script>

When I copy paste the code, embed it into a doctype using html as the type of document (see below):

The erpnext showing error:

I cannot save it at all…

Anyone have any clue what is going on?
Appreciate any feedback or comment.