You can copy the UUID which is generated in the Onboarding Base URL and provide it in the Get Validate Token API in the end and check then validity.
https://{{AuthKey}}:{{AuthToken}}@{{SubDomain}}/v2/accounts/{{AccountSid}}/isv?access_token={{token}}
{ "request_id": "15dbef467ff34a96b78e67baf63c19bf", "method": "GET", "http_code": 200, "response": { "whatsapp": { "isv": { "code": 200, "error_data": null, "status": "success", "data": { "onboarding_token_status": "VALID" } } } } }