To create a server with SIM800L, use GPRS to get a dynamic IP from your carrier. Enable TCP listening with AT+CIPSERVER=1,80. Forward incoming data to your M5Stack via serial. Since the IP is dynamic, use a DDNS service or periodically send the IP via SMS/email. Alternatively, have the M5Stack poll a cloud server for commands. SIM800L has limited capabilities, so keep the website simple (raw HTTP requests). Check the SIM800L AT command manual for TCP/IP setup details.
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