PDP authentication failed message
I have been having issues with not being able to connect to the internet (for texting and checking email). "PDP authentication failed" and "Cannot connect to the internet. Be sure your cellular data is on or connect to Wi-Fi." (or something like that) are the two messages I keep getting. Not only have I checked to make sure it's on (it is), but I've reset my network settings several times. The cell service is active (always 3-5 bars), and the SIM card is only a month old. The phone itself was purchased in December, new. I use Sakura Mobile (docomo provides the cell service), and phone service is fantastic. Any help out there?
iPhone 7, iOS 10.2.1, bought in U.S., using in Japan