Callout failed for invocable action in flow

Question

I am trying to send an API request to the external service using flow in salesforce but when I debug my flow it returns the below error

Error Occurred: Callout failed for invocable action testing3.post-vacancy-id. Expected declared response media type application/json, but got application/problem+json; charset=utf-8 for operation post-vacancy-id and service testing3

I have not specified the content-type in the header (cause I don't know how to define that in the header in flow) but I found that it will take the default content-type as application/JSON and also I have checked the body of the API request it is work fine when sending it from the postman.

I have searched regarding this but didn't find anything on the web, any help will be appreciated here.

thanks!!