So I've seen several people here had issues in the past, and there's a veritable treasure of advices.

In short: I'm despairing trying to set up a Promoted Tweet for another account.

Here's what we tried:

Making me an Ad Manager. As Ad Manager, I can create campaigns. I was tempted to also create a tweet, but when I clicked on "tweet", a red error message that "something went wrong" appeared. Not very helpful. I also didn't see any organic tweets available for promotion, let alone the one I just created.

Experimenting around, I set my account as "creative manager". Lo and behold! I could now see the creatives I just created as Ad Manager, as well as the Organic Tweets. I could even assign it to the Campaign I created! Of course, now I no longer could see the campaign itself.

Then I swiched my role back to Ad Manager. Aha! The campaign now had one associated tweet! Which I couldn't see anymore, nor did it show up anywhere else but the small little 1.

I am now Admin for the account. Now, the "Tweet" button when creating a new promotional only tweet remains greyed out and cannot be clicked.

Browsers harmed during this experiment: Edge, Opera, Safari, Chrome. First I turned off all adblockers, then I removed the plugins.

Yes, a payment method has already been created.

I am completely out of ideas here. How do you guys manage to set this nightmare up?