I find it's best to copy the URL from the bowser into the Link URL Field in case you make mistakes with the typing and in the Link Test field you can pu anything you like.

So in the example below I copied a URL http://www.walthamstowfolk.co.uk/ from the Browser into the URL field and put Walthmatow Folk into the optional text field to get the link then cut and past into the message as directed

Walthamstow Folk

I guess that if you are typing the URL you may be leaving out the http:// bit which could be the problem