This information should be in the callstack, just below the cut in the screenshot. Is Illuminate\http\Request raising the error, or something else?
Request string is formed correctly, but Laravel and Symfony http client on which it is built, rely on request headers to figure out payload type. If it worked in a previous version of NAV, but started failing in BC, first of all I would carefully compare all http headers sent in both cases - in NAV and BC. Do they match?