Tashlumin if omitted Visein Tal Umatar by Mincha of Erev Shabbos:
If one forgot to recite Visein Tal Umatar in Mincha of Erev Shabbos and only remembered by Maariv of that night, then it is disputed as to whether he is to Daven Maariv a second time as Tashlumin. Practically, this dispute has not been arbitrated and hence on Friday night he is not to Daven Maariv a second time at all, even as a Nedava.
 Admur 108:17; Michaber 108:11; Ketzos Hashulchan 28:7
 Some Poskim [1st opinion in Admur ibid; Tosafus Brachos 26b; Tur in name of Rebbe Yehuda] rule he is not required to repeat Shemoneh Esrei as Tashlumin, as in any event the reason behind for why he must repeat the Shemoneh Esrei will not be rectified, as he will not recite Ya’aleh Veyavo in the Tashlumin Shemoneh Esrei. Other Poskim [2nd opinion in Admur ibid; Rabbeinu Yona Brachos 4; Rosh Brachos 4:2; Tur in name of Sages of Province] however rule that since he did not fulfill his Mincha prayers it is considered as if he did not Daven Mincha at all, and he thus must Daven Maariv twice. [Admur ibid; M”A 108:15; Taz 108:11; See Siach Hasadeh Shaar Brachos 4:68; Eretz Tzevi 24; Chikrei Halachos 7 p. 61]
 Ketzos Hashulchan 28:7; Sor rule regarding Yaaleh Veyavo: Shaareiy Teshuvah 108:17; M”B 108:36; See Likkut Dinei Rosh Chodesh 6 footnote 29 regarding if one can be Yotzei with Meiyn Sheva
The reason: As one cannot Daven a Nedava on Shabbos. [Ketzos Hashulchan ibid footnote 20]