You can use doctorSIM for Slack without a need for a Pro account.
However, if you wish to use premium features, you'll need a Pro account.
If you have already have an account, simply link your doctorSIM account to your Slack account by typing:
- /link [email@example.com]
for example /link firstname.lastname@example.org
You'll receive a confirmation email. After you've confirmed your account you'll be able to perform premium actions.
If you still don't have a Pro account, simply sign up here