S8 plus keeps saying contact sprint to unlock service

I don't know what is causing this to happen. I have zero interest in unlocking this phone, I don't even know how to do that. I was just watching a YouTube video when i got three notifications. One saying sim card is not readable, second one saying please contact sprint to unlock your device and the last one saying invalid sim card. I have no idea how to fix this or what could be causing it. I just want my phone to go back to normal. Does anyone know what is causing this and if so can you please help me.

Welcome to Android Central! Some carrier-specific phones are more annoying about nagging you to activate it on the carrier. Are you saying you're already on Sprint? Or that you're using a different carrier's SIM successfully, even though the phone isn't carrier-unlocked? Or are you using it as a wi-fi only device?

Get a new SIM.

Try a difference SIM card to see if the issue is due to a faulty SIM. If the issue is caused by the faulty SIM, get a new one.