Welcome to the site. I'm PDtax, and will be helping you today.
If you are reporting your side income on your Federal tax return, you are paying in to Social Security on this income.
You pay in through the self-employment tax levied on your net self-employment earnings. This is added to your wages for Social Security credit.
It is mandatory, and is reported on your Federal Schedule C.
Since you are reporting gross receipts tax to Hawaii, review your Federal tax returns to see if Schedule C or Schedule SE are included in the returns. That will prove you are or aren't paying in on this income.
Thanks for asking at Just Answer. I'm PDtax.