Let me help you log in successfully using the invitation from your email, @lyudmila.
When you have an existing account in QuickBooks Online and your client uses the same or different email to invite you, make sure to sign out from QuickBooks companies open in browser windows or tabs. Then refresh your email and see if the Accept invitation link appears.
If it works, click the link and then enter your credential to log in successfully to your client's QBO account.
If the issue persists, you can follow Step 2: Check web browser issues through this link: What to do if you can't accept client's invites in QuickBooks Online Accountant.
Also, you can bookmark this future reference in case you need more idea about setting up and fixes when your client's invitations aren't in your email: What to do if invited users did not receive your email invitation.
Please tag me in your comment if you have additional questions. I'll get back to you as fast as I can. Stay safe and have a nice day!
