Are you using the link button? If so, just paste the url into the text editor itself and see if that works.
did do not sure why it didn't work
I also couldn't get it to work at first. What ended up working for me was to hover over the image and click the drop down arrow next to the link that pops up. It will give you an option for "shareable links" or something like that. Click it, then select the link next to blogs. Post that and it should work.