I created an Azure AD Application and granted API permissions like below:

I generated access token using below parameters via Postman:
https://login.microsoftonline.com/TenantID/oauth2/v2.0/token
client_id:ClientID
grant_type:authorization_code
scope:https://management.azure.com/user_impersonation
code:code
redirect_uri:https://jwt.ms
client_secret:ClientSecret

To get all App Service plans for a subscription, use the below query:
https://management.azure.com/subscriptions/SubscriptionID/providers/Microsoft.Web/serverfarms?api-version=2022-03-01

Or try this,
GET https://management.azure.com/subscriptions/SubscriptionID/providers/Microsoft.Web/skus?api-version=2022-03-01
Otherwise, for a given App Service Plan you can list the SKUs by using below query:
GET https://management.azure.com/subscriptions/SubscriptionIS/resourceGroups/RGName}/providers/Microsoft.Web/serverfarms/name/skus?api-version=2022-03-01
References:
App Service Plans - List - REST API (Azure App Service)
App Service Plans - Get Server Farm Skus - REST API