It seemed has helped me for pretty stable SMS tx, by have the most current config. In my case for Telekom .de , and brands using it, e.g. Pennymobil .de …, etc. I have recognized with SIM by Pennymobil .de I can use the Telekom .de config: Data-AP as internet.v6.telekom /dual while MMS-AP only work with internet.telekom, (IPv4 only) on proxy 109.237.176.193:8008 maybe that is in use for SMS too?
