"Enable API" not available

Hi,

I wanted to connect Mulesoft with Salesforce, but it tells me "API is not enabled for your organisation". So I checked the Community Forums for answers (most are from 2014), and there were four possible responses

1. You don't have to enable it, it is enabled by default (it isn't)
2. If you are sysadmin (I am) go to Setup > Users > YourUser > Edit > scroll down to administrator rights and check the checkbox for "Enable API" (this box isn't there, nor other options which I had seen on screenshots)
3. What edition do you use? It is only available in (...) and in developer edition by default  (I use the 30 day trial developer edition)
4. Contact support (which is not available for me, only the community)

What am I doing wrong?