Bulk Marketing with EC21 unexperienced with AT commands, but having CMS 350 errors after around 300~ successful sms deliveries

Title explains it all for the most part, but I am using a EC21 8 port that I bought from Ali. Everything is working fine just after 300 deliveries it stops delivering and I get a bunch of failed sends. Im not good with AT commands or how to use them on windows so please if you could help with if you have a solution.

I am using SMS caster with tmobile 4g LTE for the record.

P.S one of the fixes I was reading suggested depleted call credits, which is not the case these are fresh and full, and another one is incorrect SMSC, but SMS caster is reading “+12063130004” which is the correct once. What could it be?

I would also like to mention that turning off the modem and rearranging the 8 Sim cards, or turning it off and plugging into another USB port fixes the problem. Till I get to around 300-1k deliveries before it gives me CMS 350 problems.

bump please someone help me out :\

Hi @Sean_Mahoney
could you write the FW verison you are using, you need use QWINLOG tool to caputrue the log, then we can find the root cause, before that please try to send at+cfun=0 and at+cfun=1 and see what happen.


CMS are service errors. That’s nothing you can fix really. CMS 350 is typically given for no credit. You’ve probably just hit a limit on what you’re allowed to send in the time frame.

The only exception to this would be the modem trying to send message using the packet network instead of the circuit switched network without the 4G SMS settings… but really you would not get anything sent if that was the case.