unable to locate package qtmqtt5-dev

The error message "unable to locate package qtmqtt5-dev" typically indicates that the development package for Qt MQTT (qtmqtt5-dev) is not available in the package repositories of your system.

To resolve this issue, you may need to add the appropriate package repository to your system and update your package list.

For example, on an Ubuntu-based system, you can try the following steps:

1. Open a terminal window.
2. Run the following command to add the Qt 5 package repository:

   sudo add-apt-repository ppa:beineri/opt-qt-5.15.2-focal

Note: This example is for Ubuntu 20.04 (Focal Fossa) and Qt 5.15.2. You may need to adjust the repository URL and package version for your specific system.
3. Run the following command to update your package list:

   sudo apt-get update

4. Run the following command to install the Qt MQTT development package:

   sudo apt-get install qtmqtt5-dev

If the above steps do not work, you may need to search for alternative ways to install the Qt MQTT development package on your specific system.