ios – How can I fix “Unable to activate constraint ~~ ” error?

I’m trying to make ui using snapkit, but when I try to add stackview I keep getting error that says

‘Unable to activate constraint with anchors <NSLayoutYAxisAnchor:0x600001753fc0 “UIStackView:0x10380aba0.centerY”> and <NSLayoutYAxisAnchor:0x600001753a00 “UIImageView:0x103905b00.centerY”> because they have no common ancestor. Does the constraint or its anchors reference items in different view hierarchies? That’s illegal.’

When I comment out the stackview code line, everything works well, so I guess there is something wrong with the stackview.

override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = .darkGray
        
        addSubview(userProfileImageView)
        addSubview(stackView)
        
        stackView.addArrangedSubview(userHandleLabel)
        stackView.addArrangedSubview(locationLabel)
        
        addSubview(rearViewImageView)
        addSubview(captionLabel)
        
        // constraint
        userProfileImageView.snp.makeConstraints { make in
            make.top.equalToSuperview().inset(5)
            make.leading.equalToSuperview().inset(5)
            //make.trailing.greaterThanOrEqualToSuperview().inset(100)
            make.width.equalTo(userProfileImageView.snp.height).multipliedBy(1.0)
            make.width.equalTo(50)
        }
        
        stackView.snp.makeConstraints { make in
            make.centerY.equalTo(userProfileImageView.snp.centerY)
            make.leading.equalTo(userProfileImageView.snp.trailing).offset(5)
        }
        
        rearViewImageView.snp.makeConstraints { make in
            make.leading.trailing.equalToSuperview()
            make.height.equalTo(rearViewImageView.snp.width).multipliedBy(4.0 / 3.0)
            make.centerX.equalToSuperview()
            make.top.equalTo(userProfileImageView.snp.bottom).offset(10)
        }

        captionLabel.snp.makeConstraints { make in
            make.leading.equalTo(rearViewImageView.snp.leading)
            make.top.equalTo(rearViewImageView.snp.bottom).offset(5)
            make.bottom.equalToSuperview().inset(10)
        }
    }

I tried making the stackview’s constraint with equalToSuperview(), but I get Fatal error: Expected superview but found nil when attempting make constraint equalToSuperview. error, so I guess stackview is not being added…?
I also double-checked that I’m adding subview before making constraints. I just can’t figure out what causes this error.