USE FIREFOX, NOT Safari:
Using Safari 12.0 I was able to fill out the online form--tried TWICE (I was being extorted/blackmailed) but could not submit it. I turned off all my ad blockers and VPN... still could not submit. Called the FBI Sacramento (Roseville, CA.) office-- got no usable suggestions (1)come in waste 2 hrs there and back, (2) call Public Access Line *******324.
Instead I changed to FIREFOX... and that browser allowed me to file the IC3.gov report. I do not expect a reply... nor that anything is done as I was asked only for 3000usd and I did NOT pay it. But I kept the emails should FBI need them.