There is no need to have a code when sending invites to your accountant. Once you already send a request to your accountant, he/she will receives an email with the steps on how to accept the invitation.
If you need to invite your accountant, I'm happy to show you the steps, so your accountant can log in to your account and help you in managing your business. Please make sure to sign in as a master admin to add successfully.
Here's how:
Click the Gear icon in the upper-right corner and choose Manage Users.
In the Manage users page, select the Accounting firms tab. Enter your accountant email.