You can't. There's some arbitrary ranking system based on the number of posts and activity you have but 2 years and tons of posts later I've never been able to post a new idea. Spotify just wants to provide us a false sense of hope that they'll listen to us but that will never actually happen.
There's more info on how you can post a new idea in this Spotify Answer. If you haven't already, we'd recommend taking a look.
@tinyjams - if you're still having troubles after trying the steps above, we'd recommend starting a new thread in the relevant Help board, so we can take a closer look into this. We'd also suggest including screenshots of what you see and any troubleshooting steps you've tried so far. We'll be happy to lend a hand!
Hope this is helpful but don't hesitate to give us a shout if there's anything else we can help with.
Have a lovely day 🙂
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