It doesn't make any more sense in the book, no.
The book narrative is, basically, trusting Moth keeps in touch with an old childhood friend, 'Cooper', who now moves in high-flying circles, and trusts him enough to invest a 'substantial sum' in his business, which then fails, leaving considerable debt.
Cooper then starts to 'suggest' that Moth and Ray are liable to pay towards the debt, but Moth is initially more upset by the loss of the friendship and thinks they can work it out between them. Until a court summons arrives, they run out of money for a lawyer and have to represent themselves, blaming the government for legal aid reforms. Plucky underdogs being outmanoeuvred by clever barristers.
They stall until a claim is made against their farm for payment of the debt and after ten court appearances, they think they have finally found a 'magic piece of paper' that proves that their interpretation of the claim (that they're not liable for Cooper's debts) is correct, but the judge rules it as inadmissible as lodged too late, finds against them and refuses an appeal.
And as Raynor is waiting for the judge to hand down his judgement, it's the first time she registers that Moth looks seriously ill. And afterwards Moth, who is clearly a saint, goes to shake hands with the opposing barrister. And the next day gets his terminal diagnosis.
It's an effective piece of writing in establishing them as plucky underdogs worn down by the injustice of the system and a horrible illness.