There are two separate methods for adding multiple reference links as related items in other items such as tasks and issues.
The difference is that shortcuts require the full hyperlink as an input and links can be configured by a PI administrator for more simple data input to automatically create the full hyperlink. Our simple example of a link is prompting for an address and using that address to create a link to Google maps.
Link Map Configuration
Without the link configuration, the user would use Google Maps, lookup the address and then copy the full hyperlink into a shortcut rather than simply entering the address directly into PI.
Those are the two methods for adding multiple hyperlinks to a single item as related items.
Another option to evaluate before adding links and shortcuts as related items is to use a user-defined field known as an External Hyperlink. For example, you have a single site address for your projects and never need more than one. The hyperlink becomes a data field in the project status as opposed to a hyperlink in a list of related items.