SERocket Lists | GSA Search Engine Feature

I am attempting to set up SERocket lists utilising the GSA Search Engine Feature. I have followed the SERocket Guide for this very carefully: I cannot get it working.

I have reached out to SERocket support. Pathetically slow response times aside, their answers so far have only confused me. 

Their instructions CLEARLY say:

Attention: Make sure you don’t use any other Search Engine in your projects other then custom SERocket!!!

As instructed, I disabled all search engines and added the SERocket search engine, by adding the custom URL provided by SERocket and creating the stated settings. I’ve checked and rechecked it all. The setup has been done correctly (according to their instructions).

SERocket support says:

You have no link list enabled or search engine enabled. Please add the Search engine and enable it.

My understanding is that the custom URL is supposed to feed the link list (verified) straight to GSA SER. That’s the point of the whole exercise. 

I am new at this and am prepared to accept that I’ve completely screwed this up. I’m prepared to accept that the instructions are deficient and I’ve missed something important. I’m also prepared to accept that this product does not work as advertised and is a complete waste of time and money.

Looking for guidance, please.