I'm having the same problem. I followed the instructions, renewed the registered api on ffscouter several times, restarted torn pda but the error message is still there whenever I navigate to another page.
"FairFight Scouter: API request failed. Error: Invalid API key. Please sign up at ffscouter.com to use this service; Code: 6"
I tried with a limited access api too but still get the error. Also pinged the api in torn pda settings, it was successful but error persists.