These two numbers can often be confused because they are both a simple sequence of digits. Specifically, they are:
An extension number is the number one would type on their phone's dial pad to connect to a person. It is typically a three or four-digit number. When you hear, "To talk to Sales, dial extension 105" - 105 is the extension number. Extension numbers can change over time.
An extension ID is the internal identifier of an extension. This number is often a much longer sequence of numbers, e.g. "1020372920" and is intended to be used on the backend and by developers to definitively reference a specific extension. Extension IDs are immutable, and cannot be changed.
When these numbers are confused, especially when calling the API, then a number of errors often occur. The first, when calling an API in which an extension ID is provided explicitly in the URI, for example:
If that extension ID does not exist, then the platform will most often respond with a 404 error. However, some services may respond with another error. For example, the Video API will respond with a 403 Forbidden.
This is only a problem though when referring to a specific extension by its ID.
In the majority of circumstances, developers who are making API calls in relation to the extension of the currently logged in user, do not need to specify the extension ID explicitly. It is recommended that instead developer transmit the tilda "~" character to instruct the platform to infer the extension ID from the currently logged in user.
It is only really necessary to specify the extension ID when an admin is working on behalf of all users of their app.
How to find the extension ID and number? As a developer, the best way to find the extension IDs and numbers is via the List Extensions endpoint. This provides a paginated list of extensions within an account.
If you are not a developer or you don't have time to write code to figure it out, then you can discover the extension ID by navigating our Admin Portal and looking at the URL in the location bar for any given extension. In other words, you won't see the extension ID displayed on the screen, but you will it via other artifacts of our user interface.