Does the phone's WhatsApp Business number show up?

Yes, when it is connected to XBASE in coexistence. It sends through the API like the other numbers.

Does the number id change?

Not while the number stays connected. If you remove it and connect it again, it gets a new id.

List the workspace WhatsApp numbers connected through Meta's official API and get the id that goes in numberId when sending.

GET /whatsapp/numbers returns the workspace WhatsApp numbers. The id of each one goes in numberId when sending templates and messages.

GET https://api.xbase.app/api/external/v1/whatsapp/numbers

curl https://api.xbase.app/api/external/v1/whatsapp/numbers \
  -H "Authorization: Bearer $XBASE_API_KEY"

Response 200:

[
  {
    "id": "6d1f3c2a-4b5e-4f60-9a7b-8c9d0e1f2a3b",
    "phone": "5511999990000",
    "name": "Customer service",
    "status": "ACTIVE"
  }
]

Field	Type	Description
`id`	text	Number id at XBASE. Goes in `numberId`
`phone`	text or `null`	Sending number, digits only, with the country code
`name`	text or `null`	Display name of the number
`status`	text	`ACTIVE` sends. `INACTIVE` is disconnected: sends through it return `422 NUMBER_DISCONNECTED`

The list comes in the order the numbers were connected. A number removed in WhatsApp API → Numbers does not show up.

Status	`code`	When
401	`INVALID_API_KEY`	No key, wrong key format, nonexistent or revoked key
403	`MISSING_SCOPE`	The key does not have the `whatsapp:send` scope

See the full format in Errors.