Undefined citation and references altough Overleaf autocompletes them

[vapid terrace]

example of what I get on the editor and on the compiled pdf, instead of the default harvard referencing style. Thank you in advance to whoever comes forward to help 🙂

Furthermore, the same happens when I try to reference an equation by creating a label, i.e. it autocompletes the label I want to ref, but cannot compile it and just leaves the (??) in the ref.