The transfers are processed atomically (synchronously) or one by one in the background. For atomic, all fail or all succeed. For non atomic, they are processed one by one in the background and some may fail and some may succeed. The results for non atomic are sent by email to the caller. toWalletId and amount are required. Unique Id can optionally be used as a means of ensuring transactions cannot be duplicated. The unique Id must be globally unique in the system. If not provided the backend will assign a GUID for you. The fromWalletId is the source wallet for all the transfers in the list. For non-atomic, the result includes a bulkTransferId that can be used to GET the status of the transfers (progress, etc)