Outlook WebAddin is detected as contextual addin instead of ribbon addin

We have created Outlook Ribbon Webaddin. It is working as expected(ribbon Addin) and loading in top ribbon place. But for some customer, it is loading as contextual Addin.

Manifest URL : https://www.backflipt.com/app/addin/Backflipt-Beta.xml

Outlook diagnostics info :

{"host" : "Outlook", "platform": "PC", "version": "15.0.0000.0000"}

Is there any way outlook configuration affects manifest loading way?

Check the below image(blurred for security reasons) : Green color section is the plugin which is loaded as contextual addin

Seems it is not an issue with outlook mail box version or client version. I can see Cisco webex is installed in his ribbon. If it is because of version, then he should not able to install any in ribbon right.

Based on the version of Outlook that you posted in your question (15.0.0000.0000), the reason it's showing up in the horizontal bar, is because that Outlook client is significantly out of date. Please update Outlook to 15.0.4805.1000 or higher.

Please also make sure you have the following updates downloaded and installed as well (they are all required): https://support.microsoft.com/en-us/help/3114816/march-8-2016-update-for-office-2013-kb3114816 https://support.microsoft.com/en-us/help/3114828/march-8-2016-update-for-office-2013-kb3114828 https://www.microsoft.com/en-us/download/details.aspx?id=51285