You purchased the TurboTax Business Edition for 2018 from this website - https://turbotax.intuit.com/small-business-taxes/
That software you have to download and install on a Windows based personal computer, not on a Mac or online. Once installed you only access the program using the software that was installed, not online.
Why are you trying to sign onto the TurboTax online editions?
What? What did you actually purchase? TurboTax Business is a desktop software program that you do not "log in" to -- you simply open it up on your own computer. TT Business costs $169.99 and is for partnerships, S corps, C corps and multimember LLC's.
Did you purchase desktop Home and Business? That is also a desktop program which you open on your own computer--you do not "log on" to it.
We can help when we understand what you are using and what you are trying to do.