"Oh, sorry I didn't write you back! I checked 3 hours ago, and we only add the data once in our database before sending the notification to your endpoint, so everything is fine! Check if you run the same functio twice, it's an easy mistake!"

You. Fucking. Moron. You send the data 2 or 3 times (at random) every fucking time. I have nginx logs showing that, and I've fucking shown them to you TWICE. I don't fucking care if your DB is fine, check how many fucking times you POST the damn data. We're already 2 days behind schedule because you can't be arsed to check your own damn code. Ffs. How can you even be a senior developer?!