I just solved this for anyone who is having the same issue. I also tried on the app yesterday and no luck. I logged on to my personal account yesterday and linked my personal and business cards so that I could see the business card when logging in to my personal account. Today I tried again to secure message on the website with no success. However, I logged on to the app today on my business account and was able to send a secure message. I think it was the linking that allowed it to work.