Your security software may interfere with the TFTP or HTTP upload process. Disable them just for the 5-minute update window.
Finding the official firmware for older ZTE modems can be challenging, as ZTE does not host legacy consumer files on a central public portal in the same way companies like TP-Link or ASUS do. Here are the best methods to find the file safely. firmware modem zte zxv10 w300 download