Workout on Apple Watch 3

Outdoor walk in two sessions, 21 and 13 minutes translated to 25 minutes of exercise. Prior to doing the two outdoor walks, I reset the statistics as shown in the instructions. I did not carry my iPhone on the first walk because with Watch 3, the instructions said carrying it was not required. I did have it in my pocket for the second walk. The sun was shining on the first walk. It was cloudy on the second. I did not stop walking. I varied my speed during the walk.

Can you tell me what I need to do to have my outdoor walk register correctly in Activity/Exercise?

Thank you.