Based on the TurboTax Refund Advance process, what you likely saw initially was a pre-qualification or conditional approval. The final decision for the loan is not made until after the IRS officially accepts your e-filed return.
You should receive an email from WebBank (the lender) explaining exactly why your application was declined.
If your loan was denied, your full tax refund (minus any agreed-upon fees) will be deposited into your Credit Karma Money™ Spend account or the bank account you designated once the IRS finishes processing your return.