ACF图像字段采用post->ID 已上载附件的。这就是你应该传递给的$request->get_param(\'image\');

下面是我在通过API插入CPT时使用的代码。我正在发送一个带有自定义字段值的POST请求。其中一个字段是上传的图像URL，附加到CPT，标记为特色，也设置为ACF字段。

add_action("rest_insert_mycpt", function (\\WP_Post $post, $request, $creating) {
    $metas = $request->get_param("meta");
    if (is_array($metas)) {
        foreach ($metas as $name => $value) {
            # Repeatable Field (extra code just in case it helps someone)
            if( $name == \'bookmarks\' ) {
                $save = [];
                foreach( $value as $uri ) {
                    $save[] = array(\'url\' => $uri );
                }
                update_field($name, $save, $post->ID);
            }
            # Image field
            elseif( $name == \'img\' ) {
                # $value here is an URL
                $save = getImageURL($value, $post->ID, $metas[\'file_name\']);
                update_field($name, $save, $post->ID);
            }
            # Other fields
            else update_field($name, $value, $post->ID);
        }
    }
}, 10, 3);

# Upload image from URL
# @return Attachment ID
# wordpress.stackexchange.com/a/50666
function getImageURL( $img_url, $post_id, $name ){
    if( !function_exists( \'wp_generate_attachment_data\' ) ) 
        require_once(ABSPATH.\'wp-admin/includes/image.php\');
    # Upload file
    $extension = getExtension($img_url);
    $filename = "$name.$extension";
    $uploaddir = wp_upload_dir();
    $uploadfile = $uploaddir[\'path\'] . \'/\' . $filename;
    $contents= file_get_contents($img_url);
    $savefile = fopen($uploadfile, \'w\');
    fwrite($savefile, $contents);
    fclose($savefile);
    # Insert into library
    $wp_filetype = wp_check_filetype(basename($filename), null );
    $attachment = array(
        \'post_mime_type\' => $wp_filetype[\'type\'],
        \'post_title\' => $filename,
        \'post_content\' => \'\',
        \'post_status\' => \'inherit\',
        \'post_parent\' => $post_id
    );
    $attach_id = wp_insert_attachment( $attachment, $uploadfile );
    $imagenew = get_post( $attach_id );
    $fullsizepath = get_attached_file( $imagenew->ID );
    $attach_data = wp_generate_attachment_metadata( $attach_id, $fullsizepath );
    wp_update_attachment_metadata( $attach_id, $attach_data );
    # Set as Featured Image
    set_post_thumbnail( $post_id, $attach_id );
    # Generate sizes: wordpress.stackexchange.com/a/8085
    $image_sizes = get_intermediate_image_sizes();
    foreach ($image_sizes as $size){
        image_make_intermediate_size($uploadfile, $size[\'width\'], $size[\'height\'], false); 
    }
    return $attach_id;
}

# Get extension from string containing filename.ext
function getExtension($filename){
    $filename = explode(\'?\', $filename)[0];
    return substr($filename,strrpos($filename,\'.\')+1);
}

ACF图像字段采用post->ID 已上载附件的。这就是你应该传递给的$request->get_param(\'image\');

下面是我在通过API插入CPT时使用的代码。我正在发送一个带有自定义字段值的POST请求。其中一个字段是上传的图像URL，附加到CPT，标记为特色，也设置为ACF字段。

add_action("rest_insert_mycpt", function (\\WP_Post $post, $request, $creating) {
    $metas = $request->get_param("meta");
    if (is_array($metas)) {
        foreach ($metas as $name => $value) {
            # Repeatable Field (extra code just in case it helps someone)
            if( $name == \'bookmarks\' ) {
                $save = [];
                foreach( $value as $uri ) {
                    $save[] = array(\'url\' => $uri );
                }
                update_field($name, $save, $post->ID);
            }
            # Image field
            elseif( $name == \'img\' ) {
                # $value here is an URL
                $save = getImageURL($value, $post->ID, $metas[\'file_name\']);
                update_field($name, $save, $post->ID);
            }
            # Other fields
            else update_field($name, $value, $post->ID);
        }
    }
}, 10, 3);

# Upload image from URL
# @return Attachment ID
# wordpress.stackexchange.com/a/50666
function getImageURL( $img_url, $post_id, $name ){
    if( !function_exists( \'wp_generate_attachment_data\' ) ) 
        require_once(ABSPATH.\'wp-admin/includes/image.php\');
    # Upload file
    $extension = getExtension($img_url);
    $filename = "$name.$extension";
    $uploaddir = wp_upload_dir();
    $uploadfile = $uploaddir[\'path\'] . \'/\' . $filename;
    $contents= file_get_contents($img_url);
    $savefile = fopen($uploadfile, \'w\');
    fwrite($savefile, $contents);
    fclose($savefile);
    # Insert into library
    $wp_filetype = wp_check_filetype(basename($filename), null );
    $attachment = array(
        \'post_mime_type\' => $wp_filetype[\'type\'],
        \'post_title\' => $filename,
        \'post_content\' => \'\',
        \'post_status\' => \'inherit\',
        \'post_parent\' => $post_id
    );
    $attach_id = wp_insert_attachment( $attachment, $uploadfile );
    $imagenew = get_post( $attach_id );
    $fullsizepath = get_attached_file( $imagenew->ID );
    $attach_data = wp_generate_attachment_metadata( $attach_id, $fullsizepath );
    wp_update_attachment_metadata( $attach_id, $attach_data );
    # Set as Featured Image
    set_post_thumbnail( $post_id, $attach_id );
    # Generate sizes: wordpress.stackexchange.com/a/8085
    $image_sizes = get_intermediate_image_sizes();
    foreach ($image_sizes as $size){
        image_make_intermediate_size($uploadfile, $size[\'width\'], $size[\'height\'], false); 
    }
    return $attach_id;
}

# Get extension from string containing filename.ext
function getExtension($filename){
    $filename = explode(\'?\', $filename)[0];
    return substr($filename,strrpos($filename,\'.\')+1);
}