I've tried to write a variation on 'alea iacta est' but for having given someone money on ko-fi, a website that styles their content creator donations as 'giving a coffee', hence the name 'ko-fi'.
Is 'Cafaea pignerā est' a close enough translation of 'the coffee is pledged'? I chose pledged due to the nature of the giving, otherwise it looks like 'dā', 'exhibē' or 'perhibā' would be more direct translations.
First, the verb form you need is the perfect participle (in the nominative singular feminine). This is also what iacta is in alea iacta est, the perfect participle of iacere. In your case that would be pignerata, making the whole sentence: Cafaea pignerata est. That would be grammatically correct.
However, it would only work if Ko-Fi were a pawn shop that lends you money and takes coffee as collateral – because that is the sense of the English verb “pledge” which pignerare covers. Secured lending is a perfectly common business model, but it's not what Ko-Fi does.
In fact, to the best of my knowledge, you do not pledge money on Ko-Fi, but pay, send or donate it. But the somewhat silly original idea of the website – and the reason you're bringing up the potio Arabica in the first place – is that you can ostensibly “buy someone a coffee” there. And while a literal translation might not really be idiomatic Latin, I would recommend to use the verb emere (to buy) here. It's a bit of a pun on a fixed slogan anyway.
The verb is emo, emi, emptum, so the form we need is empta, making the whole sentence: Cafaea empta est (the coffee has been bought).
If you insist on “pledge” (i.e., promise), I would use a verb which happens to be the Latin cognate of “promise,” promittere, which is often used for pledging money or other valuables: Cafaea promissa est. (For extra silliness, you could say … sponsa est; spondere also means “pledge,” but in a very solemn and sanctified way, while promittere is a more quotidian word.)
