My car won't start and the security light is flashing weird

 I'm hoping someone here can help me figure this out because I've never seen this before and I'm completely lost. I have a 2015 Honda Civic that I've owned for about four years and it's been rock solid the whole time. Yesterday I went to start my car to go pick up my kids from school, and when I turned the key, the engine cranked normally for a few seconds but just wouldn't fire up. I tried a few times and the same thing kept happening. Then I noticed that on my dashboard, there's a small green key symbol or a padlock symbol that keeps flashing, and I've never noticed that light before. I think it might be some kind of security or immobilizer light. I tried using my spare key and the same thing happened, flashing light and the car won't start. I've been searching online all morning trying to understand what this means. Some forums say that the immobilizer system might not be recognizing my key, which could be a dead battery in the key fob or a problem with the receiver in the car. Other people say it could be a blown fuse or even a faulty immobilizer module. I found a link to read this article about car starting problems in the UAE, but I'm still not sure what my specific issue is. Has anyone else had this problem where their car cranks but won't start and the security light is flashing? How did you fix it? Is there any way to reset the immobilizer system myself without going to a dealership? I really don't want to pay for an expensive tow to the dealership if this is something simple like replacing the battery in my key fob. The key fob still locks and unlocks the doors fine, so does that mean the battery is okay? Any advice would be really appreciated because I'm stuck at home and I need my car back on the road as soon as possible. Please share your experiences if you've dealt with this before.