While working with Speak UI in Sitecore, I added a new Speak component rendering to my solution.
Script error for: /-/speak/v1/client/
After some poking around, I realized that this issue was occurring because of the space in my rendering name!
So while this url was giving a 404: http://redirectmanager.local/-/speak/v1/client/Redirects_Listing.js, the url with the space was working just fine:
So short of customizing the ResolveScript processor (see below screenshot) which is responsible for resolving the rendering script from your folder to the expected url with the set prefix (see below RequireJsCustomHandler setting), the work around would be to avoid spaces in your rendering names for this version and use underscores if you have to!
<!-- SPEAK HTML REQUIRE JS CUSTOM HANDLER Specifies the prefix that should trigger the HTTP request customer handler (see the customHandlers section in the web.config file). Default: /-/speak/v1/ --> <setting name="Speak.Html.RequireJsCustomHandler" value="/-/speak/v1/" patch:source="Sitecore.Speak.config"/>
Hope this helps!