Transfer Directly to Voicemail Softkey - On Mitel 6940 Phones

Hi we have Mitel 6940 phones at our offices, running on the RingCentral platform. The Mitel 6940 phones seemingly have the capability to transfer calls directly to voicemail via a "VM" softkey that appears when transferring calls (see YouTube video: https://youtu.be/Dfccs5AnSNY). However, it does not show up for us. After discussing with our RingCentral representative, it seems that this feature is not enabled for these phones on the RingCentral platform. Would be great to have this feature available as it's heavily used in our environment.