How can I open the Add Relationship drawer or the drawer from another smart action directly from a custom page?

You can automatically open the Add Relationship drawer, or the drawer of any other smart action, whenever a salesperson is directed to the details (foldout) page. To open a drawer, you pass the smart action ID using the parameter actionId. You can obtain the smart action ID from the smart actions setup page.

Here's a sample URL:

/fscmUI/redwood/cx-sales/application/container/accounts/accounts-detail?id=300100627844423&puid=CDRM_996545&view=foldout&actionId=SDA-AddRelationship-accounts