It's just a weak connection to the wireless coils. If you have a case, remove it and try, as the case may be to thick.
Also just try re adjusting the phone....wireless charging can be very finicky and it has to be placed just right on its sweet spot. No 2 wireless chargers are created equal, and their coils can range in size.
Yes it is a complete pain but that's one of the problems with wireless charging they work off of a sweet spot and sometimes the larger the phone the smaller The Sweet Spot you have the work with those who use reverse wireless charging AKA powershare on a Samsung device will know exactly what I'm talking about charging through wirelessly can be very finicky. Pulling the plug and plugging it back in does stop the lights from blinking but it doesn't prevent the problem in the long run he needs to know where your phone sweet spot is on it and trying to put it there all the time usually it's in the direct center of the phone so if you're using a stand-up charger and you want to put your phone horizontally safe for like a clock mode you want to make sure that the ends of your phone sticking out on both sides of the charger are about exactly the same so you know it's positioned the direct center as going in this position is where my problems usually have lied then we'll for many others as well where the wireless charging coils are in your phone not always match up perfectly to where the wireless coils are in a charger because the charger May wind up being taller than the phone so if you put the phone sideways for example you might only be getting a portion of the charging coils touching. No two phones coils and no two wireless charging pads coils are ever made equal the only other thing that I can say is that one of the reasons why this happens is because of cheap charger pads for wireless charging really cheap Wireless pads can get hot really fast and if a charging pad or a phone gets too warm while it's wirelessly charging it will stop and those lights will blink to let you know that there was an error when it comes to wireless charging unless you have a phone for maybe 10 years ago you can't really rely on cheap wireless chargers anymore unfortunately