Just want to close the loop here.
As @JBabichJapan mentioned, we do not allow both a website card and a website link in a single Promoted Tweet for WEBSITE_CLICKS campaigns—this is documented in our Objective-based Campaigns page. The particular Tweet you were trying to associate with the line item has both types of links—http://audi.de/DAT-Hinweis and https://cards.twitter.com/cards/18ce53z94oj/2szl4—which is why it fails.
$ twurl -H api.twitter.com "/1.1/statuses/show.json?id=809747294572740608&tweet_mode=extended&trim_user=true" | jq
{
"created_at": "Fri Dec 16 13:09:34 +0000 2016",
"id": 809747294572740600,
"id_str": "809747294572740608",
"full_text": "Dank quattro* sind Sie im Audi Q2 allen Anforderungen gewachsen. https://t.co/YCC9gAWd56 https://t.co/ebgg9yEbGk",
"truncated": false,
"display_text_range": [
0,
113
],
"entities": {
"hashtags": [],
"symbols": [],
"user_mentions": [],
"urls": [
{
"url": "https://t.co/YCC9gAWd56",
"expanded_url": "http://audi.de/DAT-Hinweis",
"display_url": "audi.de/DAT-Hinweis",
"indices": [
65,
88
]
},
{
"url": "https://t.co/ebgg9yEbGk",
"expanded_url": "https://cards.twitter.com/cards/18ce53z94oj/2szl4",
"display_url": "cards.twitter.com/cards/18ce53z9…",
"indices": [
90,
113
]
}
]
},
"source": "<a href=\"https://login.esome.com\" rel=\"nofollow\">esome engine</a>",
"in_reply_to_status_id": null,
"in_reply_to_status_id_str": null,
"in_reply_to_user_id": null,
"in_reply_to_user_id_str": null,
"in_reply_to_screen_name": null,
"user": {
"id": 29679737,
"id_str": "29679737"
},
"geo": null,
"coordinates": null,
"place": null,
"contributors": null,
"is_quote_status": false,
"retweet_count": 0,
"favorite_count": 0,
"favorited": false,
"retweeted": false,
"possibly_sensitive": false,
"possibly_sensitive_appealable": false,
"scopes": {
"followers": false
},
"lang": "de"
}