Authorization code limits / batch requests

Hello,

I'm curious about batch requests of access tokens, and/ or rate limits on that.

Specifically, when integrating with Blackbaud checkout, I'd like to already have an access code ready to go that I can pull from my database rather than having to make a request for the access code that the user has to wait on before I can make the post checkout transaction call here:

Can anyone help me out?

Thanks,

Lauren