Flash of Canon E0S 200D not working

Check the hotshoe for a stuck pin. It's not a common failure mode but it does occur, usually years later but it can occur sooner. While it can be fixed, the solution generally requires you to remove a plate from the hot shoe to "reset" the button a lot of the time. Refer to this guide for the T2i since it's the same as the SL2: Canon EOS Rebel T2i Hot Shoe Replacement. Once you remove it simply reinstall in reverse, you just need to remove the plate and can leave everything else alone in most cases but a full reset ensures it's no longer stuck. I usually remove both parts to "reset" these confused cameras.

The other thing that commonly does this is things like hotshoe accessories like bubble levels. Even though these aren't flashes and are usually light enough to not trip it on most Canon cameras a lot of these things trip the button due to how sensitive the Canon hotshoe is (yet on my a6000 with the Fotodiox TOUGH E Mount LT can have both because Sony uses a "Mi" hotshoe; the tradeoff is it's nonstandard and you need to buy from Sony or someone who licensed it); even the high-end Sony bodies like the a7 are smart enough to not lose it with "dumb" accessories" like coldshoe bubble levels. For example, I have a bubble level on a Canon DSLR (80D/T6i/ELAN 7 35mm/Others) that I need to remove for flash use and if it sticks (rare) guess what? I get to take my camera apart in the field or lose the flash for the shoot. If you have accessories like that it's probably disabling it due to the button sensor in the hotshoe. The reason I mention this is on the Sony mirrorless bodies with the Mi hotshoe (a6x00, a7, a9 and higher) the flash fires without regard or problems like this. On the a7 bodies, you can get a cage and put the flash on the Mi socket or if it's remote, put it on the cage and put the bubble level on the body and NOT HAVE AN ISSUE.

If these do not fix it, the flash circuit is dead. It can be repaired, but you need to be sure the flash capacitor is drained otherwise it BITES and you will probably throw (and break) the camera with how strong it is. Seriously, you must take precautions until you can locate and drain the flash cap; it's usually near the grip area with Canon DSLR cameras. The 35mm SLRs are a wild card to such an extent unless you know, you need to treat an open 35mm film SLR with even more respect until you know the location; it will vary from a basic 90's Rebel from a Rebel 2000; the fact they have a common area is good.