Why does my Galaxy Grand Prime from Straight Talk say invalid sim card?

[AC Question]

why do the galaxy grand prime from straight talk say invalid sim card

My galazy grand prime has been working fine for some months.. Then today it said invalid SIM card..straight talk says I have to wait til a Sim card comes in the mail.. Or either purchase one for $60 at Walmart... Is there anything else I can do..I purchased the phone from Walmart

 

[B. Diddy]

Welcome to Android Central! SIM cards, just like any other bit of hardware, can fail unexpectedly. Can you test out a different SIM card temporarily (like one from a friend's phone)?