An error occurred creating the form. See Exception.InnerException for details.

[jmcilhinney]

didnt work:
Dim tags As String = String.Join("https://live.xbox.com/en-GB/Profile?gamertag=", Form2.RichTextBox1.Lines)
doesnt work with form2.richtextbox1.text either

error:
Invalid URI: The format of the URI could not be determined.

It didn't work because you didn't do it properly. .paul. specifically said:

put the separator here

Is "https://live.xbox.com/en-GB/Profile?gamertag=" the value you want separating the parameters? Of course it isn't. Did you actually read the documentation for String.Join to see how it works? Of course you didn't. Did you even look to see what 'tags' contains after that code?

String.Join works by combining the list of values (the second argument) into a single String with each pair separated by the delimiter (the first argument). For instance, if you do this:

Dim values = {"First", "Second", "Third"}
Dim result = String.Join("||", values)

MessageBox.Show(result)

then you will see this:

First||Second||Third

So, in your case, you need to specify the bit of text that you want to separate each pair of lines from the RichTextBox in the final result when you call String.Join, then you need to concatenate that result with your original URL.