I am not able to apply a Chord Branch type connection between HSS members in my STAAD.Pro model using the Connection Design interface. I am getting a message that No connection could be defined

For Chord Branch type connections to work, you will need to assign Member Attributes to the members first. This is how you would identify which ones are CHORD type members and which ones are BRANCH type members. You may simply select the members in the STAAD.Pro model, right click and choose the Add Member Attribute option as explained in the pictures below. Once the member attributes are defined, you would then be able to apply the Chord Branch type connections