Apology for the delay.
I have got the confirmation as the HTTP endpoint didn't accept the "Accept" header this is the expected behavior. As the logic app is built on top of the Azure function .NET version and internally it using HttpContent to create the HTTP request and we do see an issue with dot net HttpContent.
If you don't have access to the HTTP endpoint and cannot change the HTTP endpoint to accept the "Accept" header then alternatively you can use the logic app (preview) which is built on top of dot net core and I tested your HTTP endpoint and I don't see any issue while using HTTP action for the logic app (preview).