Why am I unable to access a document in a subsite in SharePoint even though I have permissions?

t
1. Check the document's security and see if the permission settings allow you to access it.
t
2. Verify that the subsite you are trying to access is correctly connected to the parent site.
t
3. Ensure that the messages sent regarding permissions updates are being received and read correctly.
t
4. Check that the user is given sufficient permissions to the site containing the document before attempting to access the document itself.
t
5. Check that the permissions of the subsite match those of the parent site.
t
6. Attempt to access the document from a different device or browser.