URDF xacro-defined links not appearing in RViz2 (ROS2)

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Hello everyone,

I am building a very simple URDF model. I am using Rviz2 to test it and display it in this phase, but I can see only the main body.

I have the main model body defined in one file:

<?xml version="1.0" ?>
<robot xmlns:xacro="http://ros.org/wiki/xacro" name="mymodel">
    <xacro:include filename="$(find mymodel_descriptions)/urdf/library.xacro'" />

    <link name="body_link">
        <visual>
            <origin xyz="0 0 0" rpy="1.5707963267949 0 3.14" />
            <geometry>
                <mesh filename="package://mymodel_descriptions/meshes/body.stl" />
            </geometry>
            <material name="">
                <color rgba="0.79216 0.81961 0.93333 1" />
            </material>
        </visual>
    </link>

    <xacro:robot_wheel prefix="front_left" />
    <xacro:robot_wheel prefix="front_right" />
    <xacro:robot_wheel prefix="rear_left" />
    <xacro:robot_wheel prefix="rear_right" />

    <xacro:wheel_joint prefix="front_left" origin="0.220 0.250 0"/>
    <xacro:wheel_joint prefix="front_right" origin="0.220 -0.250 0"/>
    <xacro:wheel_joint prefix="rear_left" origin="-0.220 0.250 0"/>
    <xacro:wheel_joint prefix="rear_right" origin="-0.220 -0.250 0"/>
</robot>

and I have a very simple xacro - the one included at the top of the first file - that looks as it follows:

<?xml version="1.0" ?>
<robot xmlns:xacro="http://ros.org/wiki/xacro" name="library">
    <xacro:macro name="robot_wheel" params="prefix">
        <link name="${prefix}_wheel">
            <visual>
                <origin xyz="0 0 0" rpy="1.5707963267949 0 0" />
                <geometry>
                    <mesh filename="package://mymodel_descriptions/meshes/wheel.stl" />
                </geometry>
                <material name="">
                    <color rgba="0.79216 0.81961 0.93333 1" />
                </material>
            </visual>
        </link>
    </xacro:macro>

    <xacro:macro name="wheel_joint" params="prefix origin">
        <joint name="${prefix}_wheel_joint" type="continuous">
            <axis xyz="0 1 0" />
            <parent link ="body_link" />
            <child link ="${prefix}_wheel" />
            <origin rpy ="0 0 0" xyz= "${origin}"/>
        </joint>
    </xacro:macro>
</robot>

Any idea on what's wrong here?

Thanks in advance, Cheers, Anthares