To add to @Abi Chandra 's great response, for US and Canadian customers, the ERL will be the location address associated with the organization's default site. The location's address will be validated when selected to be the default site's location.
In order to purchase PureCloud Voice (PC Voice) Direct Inward Dial (DID) numbers, a default site with a valid location must exist in the organization. On DID number purchase, the DID number/default site address pairing is registered through Intrado (3rd party) into an emergency communications database used to appropriately route calls to local emergency call centers. This will ensure that all 911 calls are sent to the appropriate local call center based on the DID number/address pairing stored in the emergency communications database.
In the event that a DID number/address pairing does not exist in the database, the call will be sent to a national emergency call center*, where a non-local operator will handle the emergency call as appropriate.
*Calls sent to a national emergency call center may incur additional fees