why is my iphone 8 plus saying no sim

I have service with sprint, i didnt know iphone 8plus even have SIM cards, my phone is up to date on the software update. I was on the phone face time with my sister and it said in the middle of the call - call failed and then said NO SIM. I have done the ##873283# but nothing happend in order to "reprogram" as Sprint rep told me to do. i am working until 5pm this evening but I dont know how to correct this as it seems to be an issue with the phone's hardrive