curlhttpsink content-type ignored

I have a problem, i can not solve it and you are my last option.

with gstreamer version 1.14.4 i could transmit audio data to my doorbird device. now with gstreamer version 1.16.2 it does not work.

the httpcurlsink ignores the defined content-type and because of that the doorbird device does not allow to send data. see attachment.

is there a option to set the header content-type?

I hope you can help me.