How to access pages and pixels for conversion API through existing Facebook apis

I want to create an API to basically call conversion API based on the

1. to user access token through embedded signup
2. manually select event type
3. get the pages which the user will select through the access token the above are all working properly, but now I also want to get the pixels based on the page selected so I have the page id, access_token but I am unable to get any API that gives me the pixels as per the page.

I have tried:

1. https://graph.facebook.com/v21.0/me/adaccounts?fields=business_name,name,account_status,balance,currency,adspixels{name,code},amount_spent,min_daily_budget,insights&access_token=

   But it returns me: Unsupported get request. Please read the Graph API documentation at https://developers.facebook.com/docs/graph-api"

2. https://graph.facebook.com/v21.0/ad_account_id/adspixels

   but in this I have manually added the ad account id and it still didn't work, but I want to be able to call it dynamically.