I'm using a Raspberry Pi 3 (2015)

/var/log/smsd.log keeps giving:
GSM1: Checking if modem is ready GSM1: -> AT GSM1: Command is sent, waiting for the answer. (5) GSM1: No answer, put_command expected (OK)|(ERROR)|(0)|(4), timeout occurred. 1.


My /etc/smsd.conf :
# Example smsd.conf. Read the manual for a description devices = GSM1 logfile = /var/log/smsd.log loglevel = 7 [GSM1] device = /dev/ttyAMA0 incoming = no #pin = 1111

My /boot/config.txt contains:
[GSM modem on GPIO 14/15] enable_uart=1 dtoverlay=miniuart-bt


What is causing this? I’ve tried a few different wiring configurations, and I still get the same error.

It was caused by using a SIM900A chipset, which doesn't support my SIM card's 3G or 4G LTE networks.