I've tested USSD *21*xxxx# codes on PosteMobile router/sim. The connection drops for a while, and don't seems to work. I've found some logs 35 2021-12-01 11:38:28 LTE Information ERROR: Get sim card...

@TP-Link Hi, to change call diversion every week I extract the sim and I put on a smartphone to executes same codes. It works without any issue. I suspect some sort of "encoding" or some prefix...

@TP-Link VoLTE switch ON 1 2021-11-26 15:53:40 LTE Information ERROR: Get sim card number failed (0). 2 2021-11-26 15:53:40 LTE Information ERROR: 0x00000010 QMI_ERR_NOT_PROVISIONED 3 2021-11-26...

@Leoz same problem with TL-MR6500v 4G router, and TIM as mobile operator. All USSD codes return "UNKOWN APPLICATION"