You or your client may have ran into a scenario where you click start signing on the signing link and this is displayed:
From past cases, there may be an Ad Blocker enabled on your browser that is preventing the signing session from opening up. Disabling the Ad Blocker for the duration of the signing should allow you or your clients to continue with the signing. You can also try to switch to another browser which does not have an ad blocker enabled. Click the link below for instructions on how to disable the ad blocker for major web browsers.