Keeping your Pro Tumbler in an upright position with its press fit lid should help avoid leaks/spills.
Please check to see that there is a black seal inside the lid and make sure the flat side is touching the clear plastic lid and the 2 extensions around the groove are facing out.
Also, the slide piece (Black or Gray) should be slid over the mouthpiece tightly when not in use to help prevent some spillage. Please make sure it’s pushed over the hole until you hear a snapping sound.
Also, please take a look at different sides of the lid and ensure there are no cracks.