In most cases, correcting one of these 3 things will improve your pumping volume.
Size - Have you measured your nipples and are you wearing a Willow flange or container insert that is 2 - 4mm larger than your measured size? Both of these factors are critical to milk output with Willow. Follow the guidelines for sizing here to get the right size for you.
Bra - Wearing the right bra can help with volume. Your bra should hold the pumps firmly to your breasts for greater comfort and volume. We recommend wearing Willow with a full-coverage nursing bra that’s stretchy and has a flap. We have several recommended bras that work well with Willow here.
Alignment - It is important to line Willow up with your nipple before latching. Study the direction your nipple points and elongate or stimulate your nipple so you are sure of the direction it will point under suction. Keep trying, most moms master this in 5 - 7 sessions. If it is not comfortable or no milk is flowing, remove and realign.
Additional resources to consider:
Do you have tips to boost volume?
My milk volume has changed suddenly, how to I boost supply?
What is my Willow size and what sizes are available?
Do I need to wear a special bra with Willow?
How do I check if milk is flowing?