SSL issue on SIM868E

We are using the SIM868E module for connection via GSM, with internal communication over UART.

We need the SIM868E module to communicate with an HTTPS server, (using SSL), however after sending the commands AT+HTTPSSL=?, AT+HTTPSSL=1 or AT+CIPSSL=? the SIM868E module responds: +CME Error: unknown. (with CMEE level 2)

The specs note that SSL/TLS are supported by this module: (https://simcom.ee/modules/gsm-gprs-gnss/sim868e/). The firmware on the chip (requested using AT+CGMR) is Revision:1418B02SIM868E32_BLE_EAT.

We already contacted simcom support, but they haven’t answered.
How can we fix this problem?