protocol buffers - In Wireshark, create a dissector for protobuf - Stack Overflow

In some tool that I'm using, there is export to protobuf. However, when I try to use it, I'm getting an error like below.

So, in order to understand is there is problem with the full protobuf, I removed everything, except parsing the first 2 bytes:

syntax = "proto3";

package my_test
message my_test_message {
    bytes sync1 = 1;
    bytes sync2 = 2;
}

I know that the 1st byte is 0xAC (sync1) and second one is 0x13 (sync2). In wireshark I getting an output like:

Field(309):
[field name: <UNKNOWN>]
.000 1001 .010 1... = Field Number: 309
.... .100 = Wire Type: End Group (deprectaed) (4)

How to solve the issue so that I'll see sync1=0xAC (or 172) and sync2=0x13 (or 19). i.e, how can I declare in .protobuf to use single byte field?