What does "PDP authentication failed" mean?

When you try to connect to a data network on an iPhone, you might encounter a PDP authentication error message. This issue usually occurs due to incorrect settings. To resolve this, follow the instructions below, checking after each step to see if the error persists. First, enable Airplane Mode: Go to the Settings app, turn it on, wait a few seconds, and then turn it off to restore the connection. Next, restart your device to see if this fixes the problem. Finally, you may need to reset your network settings. To do this, go to Settings, then select General, tap Reset, and choose Reset Network Settings. After each step, test if network access is restored.