Hi @AndrsBeckRuiz ,
You should be able to prepend your Confluence Cloud tenant URL to the path identified by the download parameter(s) from the GET /wiki/rest/api/content/{id}/child/attachment results.
For example, if the base URL of your tenant is https://example.atlassian.net/wiki, the absolute URL to attachments will look like https://example.atlassian.net/wiki/download/attachments/....
Note the /wiki at the start of the path.
I’ve created CONFCLOUD-74412 to request the documentation be improved.
Regards,
Dugald