This is what we found on Wikipedia regarding the Mamma Mia! the Party:

Mamma Mia! (promoted as Mamma Mia! The Movie) is a 2008 jukebox musical romantic comedy film directed by Phyllida Lloyd and written by Catherine Johnson, based on her book from the 1999 musical of the same name. The film is based on the songs of pop group ABBA, with additional music composed by ABBA member Benny Andersson. The film features an ensemble cast, including Meryl Streep, Christine Baranski, Amanda Seyfried, Pierce Brosnan, Dominic Cooper, Colin Firth, Stellan Skarsgård, and Julie Walters. The plot follows a young bride-to-be named Sophie (Seyfried) who invites three men (Brosnan, Firth, and Skarsgård) to her upcoming wedding, with the possibility that any of them could be her real father. The film was an international co-production between Germany, the United Kingdom, and the United States, and was co-produced by Playtone and Littlestar Productions.

Principal photography primarily took place on the island of Skopelos, Greece, from August to September 2007. The film was distributed by Universal Pictures. Mamma Mia! held its world premiere on June 30, 2008, at Leicester Square in London and premiered on July 4, 2008, in Stockholm, Sweden, with ABBA members Benny Andersson, Björn Ulvaeus, Anni-Frid Lyngstad and Agnetha Fältskog in attendance. It was later theatrically released July 10 in the United Kingdom, July 17 in Germany, and July 18 in the United States. It received mixed reviews from critics, who praised the musical numbers and production values, but criticized the casting of inexperienced singers and campy tone. However, it was a box-office success, grossing $611.4 million worldwide on a $52 million budget, becoming the fifth highest-grossing film of 2008. A sequel, titled Mamma Mia! Here We Go Again, was released on July 20, 2018, with much of the cast returning.