Hi @paulgogu, thank you for your post! If you have a link to a Lucidchart document but do not have permission to access, you should see the following message:

You can request edit/view access to that document by clicking the blue button. If you click the arrow next to it you can specify edit or view access.

This will send your request to the owner of the document and once they accept the request, you will be granted permissions to access the document. 

For more information about sharing with collaborators, I recommend checking out this Share with Collaborators in Lucid article from the Help Center. 

Hope this helps! Feel free to let us know if you have any questions :)