How can I solve +CME ERROR: 501?

Hi everyone, my goal is to receive firmware information from the modem in the validator with AT commands.
But I got an error. The error occurs at first. Then there is no error. My output is:
Aug 2 11:10:28 val7-4k user.info asis-gprs: INF: +CME ERROR: 501
Aug 2 11:10:32 val7-4k user.info asis-gprs: INF: EC25EUXGTR03B13M1G
Aug 2 11:10:34 val7-4k user.info asis-gprs: INF: EC25EUXGTR03B13M1G
Aug 2 11:10:40 val7-4k user.info asis-gprs: INF: EC25EUXGTR03B13M1G
Aug 2 11:10:44 val7-4k user.info asis-gprs: INF: EC25EUXGTR03B13M1G
Aug 2 11:10:46 val7-4k user.info asis-gprs: INF: EC25EUXGTR03B13M1G
And it goes…
Thanks. Sincerely.

hI
501 Not Implemented means that the function requested by the client is not yet supported, similar to “coming soon, please look forward to it”