Mishnayos Kiddushin Perek 2 Mishnah 6

In the case of one who betroths two women together with an item worth one peruta, so that the value of each woman’s share was not worth one peruta, or who betroths one woman with an item worth less than one peruta, despite the fact that he later sent the traditional gifts [sivlonot] of a groom to the bride, she is not betrothed, because he sent the gifts on account of the first betrothal, i.e., the item whose value to the woman was less than one peruta, and not to effect betrothal. And similarly, if there was a minor who betrothed a woman, and he sent her gifts after he became an adult, the assumption is that he sent them on account of his betrothal when he was still a minor, and since betrothal performed by a minor is of no account, she is not betrothed.

הַמְקַדֵּשׁ שְׁתֵּי נָשִׁים בְּשָׁוֶה פְרוּטָה, אוֹ אִשָּׁה אַחַת בְּפָחוֹת מִשָּׁוֶה פְרוּטָה, אַף עַל פִּי שֶׁשָּׁלַח סִבְלוֹנוֹת לְאַחַר מִכָּאן, אֵינָהּ מְקֻדֶּשֶׁת, שֶׁמֵּחֲמַת קִדּוּשִׁין הָרִאשׁוֹנִים שָׁלַח. וְכֵן קָטָן שֶׁקִּדֵּשׁ: