The Google API for creating projects in GCP initially worked, and then they no longer worked

Question

I am developing an application that uses the google api to create projects on the google cloud platform and enable these projects to the Dialogflow api. For this reason I created a service account with the Cloud Resource Manager API and Service Usage API enabled. In sequence I send two HTTP POST requests to the service account first to the address: https://cloudresourcemanager.googleapis.com/v3/projects to create a new project and then to the address https://serviceusage.googleapis.com/v1/projects/{0}/services/dialogflow.googleapis.com:enable to enable the Dialogflow api on the new project (clearly in place of {0} I'm going to put the code of the new project returned by the previous API). Initially and for some time everything worked fine. Projects were created and with the Dialogflow API enabled. Then all of a sudden the second api to enable dialogflow gives me a resource not found error and it doesn't work anymore. I understand that the problem is the following: the API for creating new project, although it does not give me any errors and is done successfully, it does not really create the project in the google cloud platform. I add that I have a Google Cloud Identity account (required to address a parent folder when a new project is created) and an account with billing details linked to the service account. I also applied to Google to increase the maximum limit of projects allowed on the google cloud platform. I don't know why suddenly google no longer allows me to create projects via its api.