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The good news is that your interpretation of the promotion is correct. You must use your Starwood Preferred Guest Credit Card to complete $15,000 of eligible spending by the end of your first six months of Cardmembership, based on the date of your Card approval. 15,000 Starpoints will be credited to your account 8 to 12 weeks after you reach the spend threshold.

The bad news is that this offer not available by phone.

Can I apply over the phone?
A.Yes, call 1-800-223-2670. Please note: If you are applying for a special offer through an e-mail or online promotion, you must apply through the special URL link provided in the solicitation or website to receive the bonus.

I suggest you call and ask to speak with a "manager", but be prepared to start with a "supervisor". Ask for, and keep a record of, the name of every person you speak with. Mention that you attempted to apply online, and explain specifically how the process did not work. I think you'll need to say something more specific than "had trouble with submission". Keep asking politely but firmly until someone authorizes the promotion. Unfortunately there is no "Bonus ID" in the terms, and the people you speak with may not know the details of the offer and may not be able to look it up.