Question: When i open my SharePoint Designer i get the following error:

[![enter image description here](https://i.stack.imgur.com/Wc2f5.gif)](https://i.stack.imgur.com/Wc2f5.gif)

What should i do to resolve it.

Answer: 
The location where we enter the URL did make a difference for me. Please see image below.

[![enter image description here](https://i.stack.imgur.com/dQ6rN.png)](https://i.stack.imgur.com/dQ6rN.png)
Try using different connection could also solve the issue. I have experienced a similar problem with slow speed connection (a 4G modem), when using a faster connection I could connect it (another 4G network but has good coverage).