Brother Printer Connection Error 03 typically occurs when you have Proxy Settings that are allowed, however, your network doesn't need to connect. Remove your Proxy Settings to correct the issue. This error may also occur if Proxy Settings are required however they are wrongly entered. Follow the steps below to fix the issue given in this blog- Why is my Brother printer offline windows 10?
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"Connection Error 01" or "Connection Error 03" when using Web Connect. This error typically occurs if you have enabled the Proxy Settings but your network does not require it for connection. To resolve this error, disable the Proxy Settings.
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