I recently brought a new samsung galazy phone off of ebay and the sim keeps reading invalid

[AC Question]

when i brought it, it said it was unlocked but if it where actually unlocked would it still have that problem? if so how can i check the network that its locked to?

 

[B. Diddy]

Welcome to Android Central! What's the exact model number of the phone, in Settings>About Phone? Which carrier are you trying to use? Are you sure the phone supports the network bands the carrier uses? Have you asked your carrier about this? Maybe the SIM is bad, and needs to be replaced.