one time invited consultant tax consequences

If an online consultancy start up invites me to be a one time consultant to one of their

clients for 30 mins and pays me a half hour fee of $100, is that reported to IRS or is it the

consultant's responsibility to report it, if yes, on which irs form?

Self employed

Since the amount is less than $600 no form 1099-NEC is required. You report the payment as other income on your return.