client cannot accept invitation due to 400 bad request

Hi marissa-muthulin, 

Thanks for reaching out to us here.  The error your client has received, while trying to accept the QuickBooks Online user invitation, is definitely of some concern.  I would be glad to assist!

Error 400, indicates the server won't process the request for security reasons.  It's important to ensure the link begins with https.  I also suggest that you have them clear the cache on their browser, then proceed to their email and locate your invitation.  Once located, advise them to right-click on the link and open it in a private/incognito window.

If the issue persists, please don't hesitate to contact our Customer Care team at 1-855-253-1536 from Monday to Friday between the hours of 9 AM and 8 PM EST. They'll be able to review the issue in more depth and escalate it for further investigation with our Development team.

If you have any other questions, feel free to reach out again.  We would be happy to help!