Hi @AVINASHL4108

You cannot add a link property in a case type for clickable actions in Constellation. Instead use DX_components to create custom link and add your required actions on it.

Alternate solutions for your requirement "need to call an API Means Integration with external system to download the file":

1. Call your API in the post processing and manually attach your Document to Case Attachments where you can download the file.
2. Use a Check box field to run data transform on form refresh, configure your API in Data transform (Instead of link use Checkbox).

@AVINASHL4108 since you're asking for Constellation, Action Sets or Form refresh settings won't apply. This is because Constellation calls for a clear separation of concerns - you don't want to embed logic in a view. However, here is a potential approach. Again, this depends on how your API works, so I assume that at some point you might get a direct link to a document that you can simply retrieve. It may be more involved.

1. Add a new field of type URL to your case type.
2. Add this field to any view, and make sure it's displayed as read-only.
3. Set the URL accordingly. Best practice is to do this in a pre or post-processing action for your form, but you can also call a data transform directly.
4. Run your case. You should now see a clickable URL. By default, Constellation will display a link in a new tab.