Ignore the instruction signs if you want to use EA Pass+ membership discounts. Use the app to initiate the charging session, then plug in. If you want to be really safe, turn off plug & charge in the truck or on the app.
Ford has initiated their own discounted system. Blue Oval Charge Network membership will be $50/year and provide the same discounted rates at EA stations. The big advantage is you get that discount when you use Plug & Charge. I'm in a test program with my Mach E now and it works fine. Ford is supposed to roll it out soon.