“To add more staff you need to upgrade your account, upgrade with 1 click here”
I don’t agree that it’s “shady” but you can already tell that it would negatively affect conversion to directly inform people of what they’re doing, rather than waiting for them to do it and then automatically upgrading them.
If you charge on some unknown, like requests per second, then it’s better to allow the user to set an upper bound on finances anyway.