Grohe Tub spout diverter question

I purchased Grohe 13 628 Tab Spout with diverter for my new bathroom. The diverter is a push button on the spout that has a spring and is pushed down when water is running. The button is supposed to stay pushed closing the tub spout and opening the shower. I cannot make this work. As soon as I take my hand out of the button the spring pulls it up thus opening the spout. Am I doing something wrong?
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