Hello,
If the specific campaign does not have any ad group's for their campaigns with campaign subtype-App installs or App engagements, these will not be returned through the
ad_group_ad_asset_view resource. There were recent changes to the App campaigns and as mentioned in
this guide these campaigns types are required to be whitelisted. You will be able to check if the account is whitelisted, by taking a look at the campaign and its ad groups. You could reach out to your account manager to submit the whitelist request. Once the account is whitelisted to upgrade your campaigns, you will be able to pull the specific ad group ad assets data.
Please let me know if you have any further questions.
Thanks,
Bharani, Google Ads API Team

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