Starry Landscape Stacker - "Align With" feature greyed out?

Hi everyone,

I’m having a recurring issue with Starry Landscape Stacker and I’m hoping someone here might have a fix.

The "Align With" feature never unlocks for me. The photo number is always greyed out and unclickable, regardless of how many images I’m trying to stack (I've tried anywhere from 10 to 100 photos).

Has anyone else encountered this? Am I missing a step in the workflow, or is there a setting I’m overlooking?

Any advice or troubleshooting tips would be greatly appreciated. Thanks in advance!