Ifttt webhook configuration on nginx reverse proxy

I have HA behind nginx reverse proxy
I follow instruction in forum below, but when I initiate check on ifttt, HA log doesn’t receive any webhook event

When I check with https://resttesttest.com/
using method post and endpoint https://my-ha-on-internet/api/webhook/longlongtext,
then I get error message

I suspect nginx doesn’t configure correctly?
Anybody help?

Did you figure this out?

nope, i gave up
share with me if you know the solution