Service codes are not given to you just because you want one. They are given by customer support if there is a good reason to help with a problem you had with the software, etc. And you cannot apply for a refund loan.
REFUND ADVANCE
Last year for 2018 returns, certain qualified users were offered refund advance amounts on prepaid Visas at the time of e-filing, predicated on the amount of the refund and their returns being accepted by the IRS. But it had to be offered--there was no way to opt in by request. If they offer a similar program for 2019 returns, do not expect to see it until January. Since a return cannot be e-filed and accepted until the end of January, you could not receive a loan until early February at best.
https://ttlc.intuit.com/community/refunds/help/about-refund-advance/00/27333#sh-collapse1
When all of your forms and schedules are ready, you can choose to pay your TurboTax fees from your federal refund if it will be enough to cover the fees plus the additional refund processing fee of $39.99 ($44.99 in CA).
I need a service code because last year a mistake was made concerning my payment and I was told that this year would be free.
Only TurboTax Customer Support can provide a service code. You can reach them by following the steps in the below TurboTax help article.