How can I transfer calls directly to voicemail from the desktop Poly VVX450 telephone?

There are a few 'star' codes - ones where you press the * and then a series of numbers to complete a task.

The list is also on their site:
https://support.ringcentral.com/article-v2/901.html?brand=RC_US&product=RingCentral_MVP&language=en_US

The transfer to voicemail is there - yo ujust need to know what your quick flash button is designated as.

Hope this helps.