I've got you covered, @lvolk.
I'd be glad to offer my assistance with your user issue. Let's review the steps on how to invite a user and allow your user to accept it to ensure that it's working properly. Don't worry. It's a piece of cake.
Step 1: Invite your new user
Go to the Gear (Settings) icon in the top right-hand corner.
Under the "Your Company" column, choose Manage Users.
Press Add user.
Pick the user type you want for them.
Enter their name and email address and then click Save.
Step 2: Have your user accept the invite
Your user will get an email from firstname.lastname@example.org. It will include a message saying, "Ready to get started? Let's go!" and your business name. Let your user tap the "Let's go!" link. This will take them to the sign in or account creation page. They need to sign in or enter info to create a new account.
Afterward, you can check out this link to help manage your users.
After doing these steps, your new user should be able to log into the account successfully. It's my priority that you're able to get back to running your business. I value you and the success of your business. I'm only a comment away if you need me. Have a fantastic day!