Hi Kim,
Thank you for reaching out in this forum.
The reason you are encountering an error in creating app campaigns in Google Ads API is probably because you are not yet whitelisted for this feature. Creating and managing of app campaigns is only available for whitelisted customers as stated in this
guide.
Can you confirm if you have already been whitelisted? If not, you may contact your Google representative to assist you with the whitelisting. You may refer to this
blog post for more details.
Regards,
Dannison
Google Ads API Team

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