#general

I usually just say something along the lines of "the prospect decided to pause their evaluation due to busy season (or some generic reason) and intend to pick back up in a couple of months. If they're still interested in having a call I'll be sure to reconnect you. I apologize for any inconvenience and appreciate your willingness to speak with them!" So that way it sounds like they're just busy, but still interested and lets them down nicely.

not cool on the prospect to change their mind when someone is already committed to doing a reference... im sorry youre dealing with this!

I would add "I'll keep you in mind for future reference calls, thank you for your support!"

I also normally send a small gift card for coffee on me for their willingness to hop on the call

I've done similar messaging as Emily shared above. In my situations it's often our own sales rep who flagged the alarm bells for needing a reference and then puts it on hold for various reasons (e.g., client doesn't need it anymore, deal has been pushed out, etc.).