This is the 12537th most frequent Turkish word.
iddialarını
"His/her/its claims" or "their claims" (depending on context).
Here, 'iddialarını' means 'his assertions' and refers to what he claims or states.
Onun iddialarını dikkatlice dinledik.
We listened carefully to his assertions.
In this sentence, 'iddialarını' refers to 'your claims' that need substantiation.
İddialarını kanıtlayamazsan, kimse sana inanmaz.
If you cannot prove your claims, nobody will believe you.
'İddialarını' indicates 'his allegations' made during the court proceedings.