dont remeber the radarcape ports as this was two years ago when i used one. the simplest and fastest workaround i’d try now. install dump1090-mutability on the pi → connect dump1090 to radarcape → see if the aircrafts show up in dump1090 map → then connect flightairmaps to aircraft.json. this is by the way much less cpu demanding for the pi than to directly use the tcp stream from radarcape because dump1090 written in c is muuuch faster than any script like php or python is. and in addition with aircraft.json you get mlat inclusive anonymized mlat data too …
or simply use my way described above from a to z that worked for many others out of the box 