Acrylic paint begins drying whenever it is exposed to air. Thick paint does not always mean it is unusable, but it should be adjusted gradually.
Add water one drop at a time
Start with one or two drops of clean room-temperature water. Stir slowly with a clean tool, then test a small amount on the corresponding area. Add another drop only if needed.
Avoid over-thinning
Too much water can make pigment transparent and cause it to run across printed lines. If coverage is light, let the first coat dry and add a second thin layer.
Keep the remaining paint fresh
Open only the colour you are using. Wipe paint from the pot rim before closing it and press the lid down fully. During a painting session, close the pot whenever you pause.
If a pot arrives damaged or completely dry, photograph the pot and its number before contacting support.