If the ZTE modem/router is the only router in your setup, i suggest you create a manual port forwarding. I did i quick search on the net and found a screenshot of a ZTE router (don’t think it the exact same model) hope that helps.
At first go to the Roon App and under Settings —> Roon ARC write down the ip-addres of your Roon Core and the port number which is shown.
Then login in the ZTE router and take a look at the screenshot below.
You have my sincerest apologies for the delayed response here, we’ve been dealing with a higher-than-usual volume following our release and we’re working as quickly as we can to get back to everyone.
Following up on this thread, @Maarten_Duits has laid out excellent next steps for you. Are you able to create a manual port forwarding rule?
Hello no worries and thank you for reach me, I tried several times to do it, but nothing works again. I highligh that the ISP modem its plug to an Unifi UDM PRO and its imposible to set in bridge mode, don’t know if this is the issue. Thanks