Question: I'm pretty new to HTTP stuff, primarily stick to iOS so please bear with me. I'm using the httpx python library to try and send a notification to an iPhone because I have to make an HTTP/2 POST to do so. Apple's Documentation says it requires ":method" and ":path" headers but I when I try to make the POST with these headers included, headers = { ':method' : 'POST', ':path' : '/3/device/{}'.format(deviceToken), ... }  I get the error  h2.exceptions.ProtocolError: Received duplicate pseudo-header field b':path  It's pretty apparent there's a problem with having the ":path" header included but I'm also required to send it so I'm not sure what I'm doing wrong. Apple's Documentation also says to  Encode the :path and authorization values as literal header fields without indexing.   Encode all other fields as literal header fields with incremental indexing.  I really don't know what that means or how to implement that or if it's related. I would think httpx would merge my ":path" header with the default one to eliminate the duplicate but I'm just spitballing here. Full Traceback File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpx/_client.py", line 992, in post return self.request( File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpx/_client.py", line 733, in request return self.send( File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpx/_client.py", line 767, in send response = self._send_handling_auth( File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpx/_client.py", line 805, in _send_handling_auth response = self._send_handling_redirects( File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpx/_client.py", line 837, in _send_handling_redirects response = self._send_single_request(request, timeout) File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpx/_client.py", line 861, in _send_single_request (status_code, headers, stream, ext) = transport.request( File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpcore/_sync/connection_pool.py", line 218, in request response = connection.request( File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpcore/_sync/connection.py", line 106, in request return self.connection.request(method, url, headers, stream, ext) File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpcore/_sync/http2.py", line 119, in request return h2_stream.request(method, url, headers, stream, ext) File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpcore/_sync/http2.py", line 292, in request self.send_headers(method, url, headers, has_body, timeout) File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpcore/_sync/http2.py", line 330, in send_headers self.connection.send_headers(self.stream_id, headers, end_stream, timeout) File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/httpcore/_sync/http2.py", line 227, in send_headers self.h2_state.send_headers(stream_id, headers, end_stream=end_stream) File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/h2/connection.py", line 770, in send_headers frames = stream.send_headers( File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/h2/stream.py", line 865, in send_headers frames = self._build_headers_frames( File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/h2/stream.py", line 1252, in _build_headers_frames encoded_headers = encoder.encode(headers) File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/hpack/hpack.py", line 249, in encode for header in headers: File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/h2/utilities.py", line 496, in inner for header in headers: File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/h2/utilities.py", line 441, in _validate_host_authority_header for header in headers: File "/Users/User/.pyenv/versions/3.9.0/lib/python3.9/site-packages/h2/utilities.py", line 338, in _reject_pseudo_header_fields raise ProtocolError( h2.exceptions.ProtocolError: Received duplicate pseudo-header field b':method'  Request: devServer = "https://api.sandbox.push.apple.com:443" title = "some title" notification = { "aps": { "alert": title, "sound": "someSound.caf" } } client = httpx.Client(http2=True) try: r = client.post(devServer, json=notification, headers=headers) finally: client.close() 

Answer: Just need to append '/3/device/{}'.format(deviceToken) to the devServer url as the path, and the ":path" pseudo-header will be automatically set to it. that is, devServer = 'https://api.sandbox.push.apple.com:443/3/device/{}'.format(deviceToken)  Explanation: The ":path", ":method" and ":scheme" pseudo-headers generally wouldn't need to be added manually in http2 Reference: Hypertext Transfer Protocol Version 2 (HTTP/2)