What happens if you dont get approved for a car loan after your purchase?

I have bought a car two weeks ago and at the time we applied for 20k $ car loan, we deposited 8k and I was planning to deposit another 4k next week. Now we have received the letter( third party) that we are not approved for the car loan. Does that mean I have to return the car? If so why the Honda company (where we bought the car) didn't tell us anything before we receive the letter? What options do I have?

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