iPhone 6s won’t charge, keeps dying

I have an iPhone 6s and I went to charge it this morning to find that it would not charge. Every time I plugged in the charger, a pop up would appear saying this accessory could not be supported. Then, my phone died. I still attempted to plug it in when it was dead, but then it showed it was charging and my phone came back to life. However, it was at 1% for about twenty seconds, then it died again. This keeps repeatedly happening and I do not know what to do.