How can I fix this error? I can't call my API from the backend
The owner of the API has to allow access from the origin you are trying to access from.
If you own the API you are trying to access, look into how you can allow CORS access from a specific origin on the platform that your API is built on.
If the owner of the API is someone else within your organization, you may be able to talk with them and arrange for them to allow you access.
If the owner of the API is not within your organization, you may be out of luck.