The Gemorah in Chagigoh 8b states that the Mitzva of simcha on Yom Tov, ושמחת בחגך is done with Korbanos שלמי שמחה.
This is seemingly contradicted by our Gemorah which states that on Yom Tov Rishon when there cannot be Shalmei Simcha, we fulfill our obligation with clean clothes and old wine.
The Shaagas Aryeh explains that the Mitzva of Simcha includes all Simcha, not just Shalmei Simcha. Therefore when we don’t have Shalmei Simcha, we may fulfil our obligation with clean clothes and old wine.
He explains the Gemorah in Chagigoh which states that the Mitzva is with Shalmei Simcha, that the Mitzva is to be happy on Yom Tov with all possible types of Simcha. Since Shalmei Simcha is a type of Simcha, we must engage in that form of Simcha on Yom Tov as well.