Respondent.io bait and switch?

Has this ever happened to anybody else? I completed a study advertised at $100, and after completing it they send a message saying "the advertised payment was an error" and sent $30 instead.

This is unacceptable. What recourse does one have here?

Wednesday, March 31st, 2021

[name redacted]

Hello,

I apologize for the delay in payment. There was an error in the set-up of this study, advertising the incentive of $100. Unfortunately, this incentive price is incorrect due to the method of the study and amount of time to complete each session. This study incentive has been updated to the correct pricing of $20 however, we do recognize that this change may be disappointing so we will be adding a $10 tip on top of the $20 incentive. We sincerely apologize for the error and any issues.

Thank you.