ANTLR4 version 4.13.2, C++ target.

I have a Lexer and Parser rules as below.

Lexer:
enter image description here

Parser:
enter image description here

I use the command antlr4 -Dlanguage=Cpp -listener -visitor -o generated/ -package spec SpecLexer.g4 SpecParser.g4 to generate code.

Then, I have a program:

antlr4::ANTLRInputStream input("Test: { } ;");
spec::SpecLexer lexer(&input);
antlr4::CommonTokenStream tokens(&lexer);
tokens.fill();
for (auto token : tokens.getTokens()) {
    std::cout << token->toString() << std::endl;
}
spec::SpecParser parser(&tokens);
antlr4::tree::ParseTree* tree = parser.root();
std::cout << tree2->toStringTree(&parser) << std::endl;

When I try to run it, it always report the error:
enter image description here

I cannot understand, the lexer seems to work fine, but parser cannot always match the first token.

I cannot understand, the lexer seems to work fine, but parser cannot always match the first token, why???