I'm trying to access the partner API on a salesforce environment, but I can not find the API Enabled option. I did find it on an other environment.
How can I enable/add this option?
You don't specify your edition in your question, but that's likely the cause of this issue.
See Salesforce Editions with API Access.
To use the API, your organization must be on one of the following 4 editions (the API is enabled by default):
- Enterprise Edition
- Unlimited Edition
- Developer Edition
- Performance Edition
Editions with no API Access
- Contact Edition
- Group Edition
- Professional Edition