Are you using the right chat_id and including your bot's token after "bot" in the address? (api.telegram.org/bottoken/sendMessage)
This page explains a few things about sending (down in "sendMessage" section) - basic stuff, but I often forget the basics.
To quote:
In order to use the sendMessage method we need to use the proper chat_id.
First things first let's send the /start command to our bot via a Telegram client.
After sent this command let's perform a getUpdates commands.
curl -s \
-X POST \ https://api.telegram.org/bot<token>/getUpdates \ | jq .
The response will be like the following
{ "result": [
{
"message": {
"text": "/start",
"date": 1435176541,
"chat": {
"username": "yourusername",
"first_name": "yourfirstname",
"id": 65535
},
"from": {
"username": "yourusername",
"first_name": "yourfirstname",
"id": 65535
},
"message_id": 1
},
"update_id": 714636917
} ], "ok": true }
We are interested in the property result.message[0].chat.id, save this information elsewhere.
Please note that this is only an example, you may want to set up some automatism to handle those informations Now how we can send a message ? It's simple let's check out this snippet.
curl -s \
-X POST \ https://api.telegram.org/bot<token>/sendMessage \
-d text="A message from your bot" \
-d chat_id=65535 \ | jq .
Where chat_id is the piece of information saved before.
I hope that helps.