That email already exists in the Bob system, as your new hire was already using Bob with his previous employer. Since it is associated with a different account you are not able to add it to your account.
Here are a few different suggestions on how to solve this:
1. Provide your employee with an organizational email
Generally, it's best to set up a Bob account using an email issued to an employee by the company, instead of a personal email. If possible, providing an organizational email would be a "quick win".
2. Ask your employee to contact their previous employer, requesting to delete their record or update the email they hold on file.
Understandably, this isn't the most convenient option but since this is a request to remove personal data, it's best to be initiated by your employee.
3. With your employee's consent, we can contact their previous employer on their behalf
In this case, your employee would have to write to us (separately, or in continuation as CC to this thread) providing consent for HiBob to reach out to their previous employer asking them to update their records or delete them if possible.
4. Using the same email, with a "+"
Gmail has a great feature, where you can add a "+" to your email, and most services will see the email address as unique but all emails will still go to your specific account.
For example, you could try using the email abc+1@gmail.com
In the end, some of the above options are easier than others but please consider which option would work best for you and your employee.