I have created a new AdWords account via my MCC account. About this I have created a campaign and an ad group. All this can be read out well via the API.
But if I want to create an ad, I get the following undocumented errors.
[AdError.INCOMPATIBLE_WITH_RESTRICTION_TYPE @ operations[0].operand.ad]
In another AdWords account, which is also managed by our MCC, this is possible without any problems.