Hello @MACS_ENGINEER ,

Welcome to our community.

The router doesn't distinguish between single-network or multi-network SIMs based on the carrier's business model—what matters is the technical compatibility. Here's what determines compatibility:

1. Network Types and Bands:
The most important factor is whether the multi-network SIM's supported bands match what your TL-MR6400 supports. You should:
• Check with your SIM provider about which network types (3G/4G) and frequency bands the multi-network SIM supports in your area
• Verify these against the TL-MR6400's specifications on the TP-Link website to ensure they align

2. SIM Card Size:
The TL-MR6400 uses a standard SIM card slot, so ensure your multi-network SIM is the correct size (or use an adapter if needed).

3. APN Settings:
Multi-network SIMs may require specific APN configurations. Since you're seeing the "prepared" status but no internet connection, this is likely where the issue lies. You should:
• Contact your multi-network SIM provider to get the correct APN settings
• Manually create an APN profile in the router at Advanced > Network > Internet/Mobile WAN

The data roaming prompt you're seeing is normal for multi-network SIMs, as they switch between carriers. As mentioned in my previous response, you should confirm with your SIM provider whether enabling data roaming will incur additional charges for your specific plan.

  @MACS_ENGINEER ,

Here are some suggestions regarding your concerns:

Regarding Data Roaming and Charges:
Enabling data roaming allows you to stay connected when the SIM switches between different networks. To utilize the data roaming function on your TP-Link 4G LTE Router, ensure your mobile service provider has an active data plan that supports this feature.

Important: Data roaming may incur extra charges, with rates varying by mobile network and provider. Since you're using multi-network SIMs specifically designed to switch between carriers, you should contact your SIM provider to confirm whether enabling data roaming will incur additional charges in your specific use case, as multi-network SIMs often have different billing structures than standard SIMs.

You can enable Data Roaming through the Web Interface:
1. Log in to the Web UI at http://tplinkmodem.net
2. Navigate to Advanced > Network > Internet/Mobile WAN and enable "Data Roaming"

Regarding the IP Address Confusion:
The router's LAN IP (192.168.1.1) and the SIM's static IP are completely different things and serve different purposes:
• Router LAN IP (192.168.1.1): This is the internal/local IP address used for your private network to access the router's settings
• SIM Static IP: This is the public WAN IP address assigned by your carrier for internet connectivity

You do NOT need to change the router's LAN IP to match the SIM's static IP. They operate on different network layers. The static IP from your SIM will be automatically used as the WAN IP for internet connectivity.

Additional Troubleshooting:
If data roaming doesn't resolve the issue, try these steps:
1. Go to Advanced > Network > Internet/Mobile WAN page, and select another APN profile in the drop-down list to see if it works
2. If no profile works, click "Create Profile" to create a profile manually (confirm the correct APN parameters with your SIM provider first)
3. Change Network Search from "Auto" to "Manual" and select your ISP manually