Same issue here. As soon as you hit the ‘request to book’ button after filling your credit card details, an error will occur with this message: “Let’s try that again. This can happen if your account wasn’t created directly on Airbnb. In order to finish booking, please remove the coupon”.
I created my account directly on their site using my email and not with those social media auth methods (Faceboook, Google). Their platform seems buggy and if you check your invite points or travel credit, no more points available and that discount coupon will be shown as ‘spent’