Advance online publications generally refers to journal articles before they have been printed. They will not have a volume number, issue number or page number. To indicate this you should include the phrase “Advance online publication” before the doi.
Gregor, C., Davidson, S., & Hingley‐Jones, H. (2014). The experience of gender dysphoria for pre‐pubescent children and their families: A review of the literature. Child & Family Social Work. Advance online publication. doi:10.1111/cfs.12150