Sorry--you cannot get a refund loan unless you enter the proper documents into your tax return, and pay stub will not suffice. There may be other places that let you do that with a pay stub, but not TurboTax.
https://ttlc.intuit.com/community/refunds/help/about-refund-advance/00/27333#sh-collapse1
CAN I USE MY PAY STUB TO PREPARE MY TAX RETURN?
Please do not try to use your pay stub to prepare your tax return. It will not match the W-2 that you will get from your employer in just a few short weeks. Your employer has until the end of January to give you your W-2. By waiting for your W-2 you will be able to file accurately. If you try to guess what goes in the W-2 “boxes” and mess up your return, you will need to amend. It takes about 4 months to amend a tax return. The IRS will not be accepting 2019 returns until the end of January — so you can wait for your W-2. If you are hoping to get a quick tax refund by filing early, using your pay stub might have the opposite result. Your tax return will not match the W-2 reported to the IRS by your employer; this may result in rejection of your return — or if accepted, could actually delay your refund for months. And, if you are hoping to get EIC or the refundable amount of the child tax credit, your refund will not be released until late February anyhow. It is much wiser to wait for your W-2 and file correctly.