"Please pay the money today."
To me it sounds a bit blunt, but more in the sense of “today it’s your turn to pay”. Maybe the speaker and addressee are members of a group who frequently eat out together, but the addressee never volunteers to take the bill. After everybody else has already paid twice, finally somebody comes forward and tells the addressee that today it’s their turn to pay.
The reason for this feeling is that -が marks a non-topic subject. This indicates that the subject here is new information: The sentence is telling you who is paying today, not what is to be done or when to do it. I feel this is especially true in an imperative clause, where the subject is actually already implied by the mere fact that it is an imperative.
(Disclaimer: I’m far from a proficient Japanese speaker. Much of my gut feeling here is transferred from Korean, which also has a topic-subject distinction working – in my experience – in pretty much the same way as it does in Japanese. So I personally feel fairly confident in trusting my feeling here, but still, take it with a grain of salt.)
さくじつ (wink) I discovered that my gold standard for bilingual dictionaries—audio, multiple glosses, example, flash cards, and other GOOD STUFF—SpanishDict has feet of clay, using such hoary old nonsense from MONOLINGUAL English dictionaries. I mean, how many seconds does it take your ear to master the four "Spanish vowels" used in Japanese? Now teaching your mouth to produce them takes constant vigilance. The most common vowel in English, after all, is the schwa (ə).
The Pronunciation columns are a waste of screen real estate. Give me IPA (or phonemes) or give me death!