The Rambam wrote in Mishna Torah that marriage by money [e.g., a ring] is derababan (from the scribes), since it is learned by a gezera shava (a principle of learning law from the text, but not statd in the text). Some commentators claimed the Rambam really meant that it is from the Torah. However, the Ramban (Nachmanides) in Sefer ha’Mitzvot Root 2 brings a question and answer of the Rambam about this issue. The Rambam was asked directly about this and reiterates the claim the marriage by money is from the scribes. He even goes on to explain that everything learned by the 13 midot is from the scribes unless it says openly in the gemara that is ''from the Torah.'' that is it has to say those exact words. Even if it says, "It is a Law to Moses from Sinai," that does not mean it is from the Torah. Rather, it means that Moses derived it from the Torah.-----------------------------The רמב’’ם wrote in תורה משנה that marriage by money is דרבנן since it is learned by a גזרה שווה. On the side some commentators claimed the רמב’’ם really meant that it is from the תורה. However, the רמב''ן in ספר המצוות שורש ב' brings a question and answer of the רמב’’ם about this very same issue. The רמב’’ם was asked directly about this and reiterates the claim the קידושי כסף is דרבנן. He even goes on to explain that everything learned by the 13 מדות is דרבנן unless it says openly in the גמרא that is ''from the תורה.'' that is it has to say those exact words. Even if it says הלכה למשה מסיני, that does not mean it is from the תורה. Rather, it means that משה derived it from the תורה.