Here in the specification this sample which says can be converted to cbor on cbor.me when copy/paste it gives an error on the comma with nothing after it at the “arg”: h’0061736d01000000’,
A typical request would be (written in CBOR diagnostic notation, which can be checked and converted on cbor.me):
55799({ “content”: { “request_type”: “call”, “canister_id”: h’ABCD01’, “method_name”: “say_hello”, “arg”: h’0061736d01000000’, }, “sender_sig”: h’DEADBEEF’, “sender_pubkey”: h’b7a3c12dc0c8c748ab07525b701122b88bd78f600c76342d27f25e5f92444cde’ })
(“sender_sig”: h’DEADBEEF’ 
)