What is an in-home support services supplemental plan?

[LeeM]

You would first need to be an in-home support services (IHSS) provider who pays sales tax.

IHSS providers only receive a supplementary payment if they paid a sales tax on the IHSS services they provide. 

It is basically a reimbursement of sales tax you paid on any IHSS services.

So only if you have supplementary payments should you enter anything there.