I understand you need to get the codes via the mobile number. @Newcs23. Instead of a phone number, let's use the email to obtain them.

Have you tried using another number? So we can identify if this is an issue within QuickBooks Online.

Additional rights granted to accountant users allow them to cancel reconciliations, reclassify transactions, and write off invoices. Moreover, if you have an email address, you can use them to get the verification code from QuickBooks Online. 

Here's how:

1. From the home screen, click on the Gear Menu, and beneath the column heading labeled Your Company select the Manage Users tab.
2. On the Manage Users page, click Invite Accountant to open a new invitation.
3. Enter the name of your accountant and email address into the text boxes and click Next.
4. Click Finish. Your accountant will get an email with a link to your QuickBooks.

Please check out this article as your reference: Add accountant users in QuickBooks Online. Removing an accountant is available on this page.

We are always ready to support and guide you through every task in QuickBooks Online. We are happy to serve you.