@Shebnem What is the model no. and hardware version of your TP-Link modem? If you mean login password of the web interface, you could try admin in lower case.

@Wilsonchav2003_ You may try a factory reset by holding reset button for 10s

@Geza83 Hi, NX510v is a model for ISPs only, and we don't have much information about it, and usually ISPs might have default CWMP Settings on the product. Besides, you could check Internet IPv4...

@jacquot73 Hi, I am afraid the MR400 or our other LTE gateway routers don't support to use SMS by API or commands.

@fabras Hi, please follow this guide for troubleshooting the remote management issue: How to troubleshoot if remote management does not work on LTE Gateway Router with 3G/4G Router mode

@Euphy Hi, APAC version and EU version are sold in different countries or areas, and EU version of MR6400 doesn't support LTE band 28. Here are the network type and bands supported by MR6400 EU V5.30: