Go to Network → WAN press Edit on the mobile interface and make sure PDP type is set to IPv4/IPv6. You can try changing it to IPv4 only and IPv6 only and see if that helps.
Ensure you have the correct APN set up for the sim card, if you have it set on Auto currently, try to input it manually according to your carrier.
Go to Network → Mobile → General and on the bottom of your page you will be able to edit the APN configuration, turn off Auto APN and press Add new, then you will be able to type the APN in.
Go to Network → Network Selection and change Operator selection mode to Manual, then press Scan for operators, after a while you will see a list of operators that are currently available. Select an operator that is a partner of your local carrier (this information should be on your carrier’s page)
Please let me know if this solves the issue. And if possible, let’s keep the communication in English further on, so nothing gets misinterpreted in the translation.
If nothing helps, please clarify your device’s order code to me, so I could check if the router supports the bands used in Croatia. If you will send a screenshot, please be careful and don’t include sensitive information such as the serial number or MAC address.
You can find the product code of the device on the box itself
Or in the WebUI go to Status - > System and there you can see the Product code