I've played this around for you.

First of all, GD (and even Imagick in its default operations) doesn't support perspective transformations - which is what you need to make the banner look like it's part of a 3D surface.

You cannot realistically get perspective distortion with GD, unless you manually do it with polygon fills which I would skip for sure, too complex...

However with Imagick I used distortImage() as in the comment Chris Haas mentioned with Imagick::DISTORTION_PERSPECTIVE.
I've created this code:

function mergeWithPerspective(string $basePath, string $bannerPath, string $outputPath): void {
    $imagick = new Imagick(realpath($basePath));
    $banner = new Imagick(realpath($bannerPath));

    // Resize banner to fixed dimensions for consistent perspective mapping
    $banner->resizeImage(230, 300, Imagick::FILTER_LANCZOS, 1);

    // Map corners of the banner to positions on the truck's black panel
    $controlPoints = [
        0, 0,        496, 145,  
        230, 0,      715, 163,  
        0, 300,      495, 407,  
        230, 300,    712, 375   
    ];

    $banner->setImageVirtualPixelMethod(Imagick::VIRTUALPIXELMETHOD_TRANSPARENT);
    $banner->distortImage(Imagick::DISTORTION_PERSPECTIVE, $controlPoints, true);

    // Composite the distorted banner onto the truck image at a specific offset
    $imagick->compositeImage($banner, Imagick::COMPOSITE_OVER, 507, 110);

    $imagick->writeImage($outputPath);
    $imagick->clear();
}

I applied a perspective distortion on the banner and tried to placed it realistically.
The downside of this as you can see that you have to define a starting X and Y coordinate with compositeImage() as well as creating the necessary control points with $controlPoints.

This is the result:

I've created a github repository for this:
https://github.com/marktaborosi/stackoverflow-79562669

The source images are in:
src/source-images

The processed image is in:
src/processed

Hope this helps!