I struggled over this for a while and then found the answer.
Say you have a Blueprint and within your BP you have a widget. If you want to call a function that’s in your widget from your blueprint, then it’s slightly more complicated than just dragging the widget component into your function from the Components window. There are two extra steps
Step1 – drag reference from Components Window
Step2 – Get User Widget Object
Step3 – Cast to your widget BP
Step4 – Call your function in the widget BP