In your Google document, click on Share in the upper right corner of the screen.

Set your desired access options, then click on Copy. If you’re embedding a document with organization or restricted access, please read the dedicated sections below.

Restricted Google documents require login in order to be viewed and embedded.
At this time, Google’s support to external authentication is limited and it may happen that, when trying to embed restricted documents, Google login screen doesn’t show up and instead a generic error is displayed.
403. That’s an error.
We’re sorry, but you do not have access to this page. That’s all we know.

To fix this, you can follow this procedure:
Temporarily disable the restriction OR copy the link of any unrestricted Google file.
It has to be compatible with the embedder you’re using.
Example: Google Sheets Embedder 👉 use a Google Sheets unrestricted link
Embed the link or refresh the page if you’re not changing link
Click on Access and log into your Google account. You will be redirected to the external service (e.g. Google Sheets).
Go back to the page where you embedded the document (in either Jira/Confluence or monday.com)
You can now enable the restriction again or swap back to the file you originally intended to embed.