It seems this was also posted to SO:
https://stackoverflow.com/q/52210169/4690866. I provided an answer there.

On Thu, Sep 6, 2018 at 12:57 PM 'Carl Mastrangelo' via grpc.io <
[email protected]> wrote:

> This error comes from the ALPN TLS extension, which you need your SSL
> endpoint to support.  If you are using NPN, it is unlikely you will be able
> to connect.
>
> On Thursday, September 6, 2018 at 11:06:02 AM UTC-7, [email protected]
> wrote:
>>
>> Hello, I am connecting to a server which has TLS support with SSL certs.
>> I am getting a SSL Handshake error on *Android* app client. I also use
>> *useTransportSecurity()* to deal with TLS negotiation type. Is there any
>> workaround to get away with this error without certificate pinning?
>>
>>
>>
>> ----
>>     Caused by: java.lang.RuntimeException: protocol negotiation failed
>>
>>         at
>> io.grpc.okhttp.OkHttpProtocolNegotiator.negotiate(OkHttpProtocolNegotiator.java:96)
>>
>>         at
>> io.grpc.okhttp.OkHttpProtocolNegotiator$AndroidNegotiator.negotiate(OkHttpProtocolNegotiator.java:147)
>>
>>         at
>> io.grpc.okhttp.OkHttpTlsUpgrader.upgrade(OkHttpTlsUpgrader.java:63)
>>
>>         at
>> io.grpc.okhttp.OkHttpClientTransport$2.run(OkHttpClientTransport.java:474)
>>
>>         at
>> io.grpc.internal.SerializingExecutor.run(SerializingExecutor.java:123)
>>
>>         at
>> java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
>>
>>         at
>> java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
>>
>>         at java.lang.Thread.run(Thread.java:764)
>> ----
>>
>>
>>
>> And this is how I generate my channel :
>>
>> ManagedChannel mChannel = OkHttpChannelBuilder.*forAddress*(host, port)
>>         .useTransportSecurity()
>>         .build();
>>
>>
>>
>>
>>
>> Appreciate your time and help.
>>
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