Payment terms are set by the contract. As a rule the terms of the contract will be written in favour of the employing party, if you don’t like long payment terms, condition precedents for payment, etc. then negotiate fairer terms.
There’s no point signing up for work where there may be a condition precedent for payment which realistically can’t be achieved until after the first valuation period, or payment terms extended into 60 days – can you maintain positive cashflow in this scenario, are you happy acting as banker for the main contractor?
Most contracts are heavily amended so read & understand the payment process, again if the terms are unfair negotiate. If you don’t follow the protocol, then you could risk your payment for that period.
There is nothing wrong in negotiating, if the terms are heavily weighted in favour of the main contractor & they will not amend to make them fairer to both parties what does that say about the main contractor & their attitude toward their supply chain?
Its OK to walk away. There are other projects, other main contractors don’t put your project / business at risk by signing up to unfair payment provisions.