You only need to be registered as a professional corporation if you are a C corporation. As a PC you would be required to pay taxes at a rate of 35% regardless of level of income.
As an S corp the corporation does not pay any taxes. The income flows through to your personal return and you claim the income there.
Registering as a PC does not apply here since you are an S corp. If at some time you disengage the S corp election you will have registered as a PC, not as a straight C corp.
For now though, do nothing.
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