Tricky part of any project is financial reporting. Basically it is just collecting evidence about money transfers, but you have to meticulous in documenting all expenses including tenders, project team expenses, expenses not procured etc.
The first evidence should start when project idea is accepted, elaborated with or without partners, communication and meetings begin, collection of information and data, and in process of application. For some projects just elaboration of project, by external expert or company, is considered as eligible expense. For other calls for proposals all previously mentioned expenses are eligible, but have to be documented.
So, you need to start early. If you don't want to bother with such an evidence then the simplest solution is engagement of consultant for preparation of project, application documents and conduction of application procedure.