No, it's not an indication of a successful SQL injection. Literally the error means that your request doesn't conform to the Uniform Resource Identifier (URI) standard syntax (RFC 3986, 3.):
\_/ \______________/\_________/ \_________/ \__/
| | | | |
scheme authority path query fragment
It's unclear what is giving the error.
If it's your browser, the request doesn't even reach the server. In HTTP(S) the server sees the authority part on the
Host: header and the path and query parts in the (GET / POST) request.
If the request actually goes to the server and the server is unable to handle it, the server would probably response with the
400 Bad Request error, instead.
Some web application firewall (WAF) could respond with a
Malformed URL error, but it's more likely to give
403 Forbidden without revealing the attacker what's the exact security rule that was fired.
You could even be behind a proxy / NGFW / UTM that blocks malformed request from leaving your network. Such an appliance would probably show the error directly to you.
In any case this doesn't look like you have succeed at all. Also, organizations having bug bounty programs have probably already fixed the most obvious vulnerabilities. You would need to come up with something a lot more sophisticated. Frankly, if you were capable of that, you wouldn't be asking this question here.