Error message Could not save to favorites - Real Estate sellers

Am wanting to save a seller (Real estate agent) that has many listings as I am waiting on them to list a property for sale for me and want to get notified when the listing when is live. I click the Save this seller button when on their listings page and get the Choose frequency of being emailed modal pop up and I make the choice, but then get the red error message Could not save to favorites. I have tried but get this problem with all Real Estate agents, but not regular sellers. If it's not possible to do this, why is the Save this seller button there? TM Store listings don't have the Save this seller button, so if it's not something that's supported for whatever reason, why is the button there. If it is supported, then it's not working.