Adding more Self-leveling product to floor

Do you have to sand down self leveling product to add more product on top to achieve width of matching existing floor?

The first layer is cracked and needs to be thicker/higher by the register and levelled out smoother in lots of places.

Does anyone recommend putting down another adhesive layer in-between self leveling product? I have had conflicting advise.. manufacturer instructions doesn't say about add more adhesive before adding a second layer of Self-leveling if needed??
Thank you!

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