Not able to create preview for customized asset feed spec preview - facebook-graph-api

Question

I am using the following asset_feed_spec bean:
"asset_feed_spec": {
"ad_formats": [
"CAROUSEL_IMAGE"
],
"asset_customization_rules": [
{
"customization_spec": {
"publisher_platforms": [
"facebook"
],
"facebook_positions": [
"story"
]
},
"carousel_label": {
"name": "labelStory"
}
},
{
"customization_spec": {
"publisher_platforms": [
"facebook"
],
"facebook_positions": [
"feed"
]
},
"carousel_label": {
"name": "labelNormal"
}
},
{
"customization_spec": {
"publisher_platforms": [
"instagram"
],
"instagram_positions": [
"story"
]
},
"carousel_label": {
"name": "labelStory"
}
},
{
"customization_spec": {
"publisher_platforms": [
"instagram"
],
"instagram_positions": [
"stream"
]
},
"carousel_label": {
"name": "labelNormal"
}
}
],
"bodies": [
{
"text": "hiiiiiiiiiiiiiiii123"
}
],
"call_to_action_types": [
"LEARN_MORE"
],
"carousels": [
{
"adlabels": [
{
"name": "labelNormal"
}
],
"child_attachments": [
{
"description": "testing",
"picture": "<picture_url_here>",
"link": "www.google.com",
"name": "test"
},
{
"description": "testing",
"picture": "<picture_url_here>",
"link": "www.google.com",
"name": "test"
},
{
"description": "testing",
"picture": "<picture_url_here>",
"link": "www.google.com",
"name": "test"
}
]
}
],
"descriptions": [
{
"text": "test"
}
],
"link_urls": [
{
"website_url": "hi.com"
}
],
"titles": [
{
"text": "hiiiiiiiiiiiiiiii123"
}
]
},
"object_story_spec": {
"page_id": "<page_id>"
}
}