API to merge call into conference call

When we have two (or more) calls ongoing, how do we conference/merge them together (in the UI or programmatically)?

When there are two active calls, here's an example of what we see:

• In Ringcentral Embeddable UI:

.

• Compared to the Ringcentral Phone UI which has a 'Add' button that allows adding the other call to the conference:

It would be ideal to also have the ability to programmatically perform this conferencing action.

We are using the following URL to load the Embeddable:

https://apps.ringcentral.com/integration/ringcentral-embeddable/1.0.3/adapter.js?appKey=...snip...&appSecret=...snip...&appServer=https://platform.devtest.ringcentral.com&enableFromNumberSetting=1&disableConferenceCall=false&disableActiveCallControl=false

Could this be due to Permissions? I didn't get any errors indicating lack of permissions, but here's what is currently configured for the client I'm using:

Start with the RingCentral Embeddable adapter URL and its active-call controls, then investigate whether the widget or API exposes a merge/conference action and whether permissions affect it. Done means the supported UI or programmatic path for merging two active calls, including its permission behavior, is defined and documented or implemented.