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"
}
}
}
}
}