TL;DR: it is quite possible that this is legitimate, but it just may be a well-disguised scam. Apply your usual cautionary procedures.
I have reviewed for internationally less visible research councils before; there may be some reasons why they invite international reviewers - for instance, some ambitious science minister wants to raise the scientific profile and quality of the research and thus invites well-known and -respected scientists to the panel to improve decision quality and visibility.
Without prejudicing your further investigations, there is a possibility that this is legit. Depending how the expense is paid (per report or in total) you would not have to read just a single 10-15 page report, but 10 of them; that can be tiresome (although some comments say itpayment may be per report, which would, in turn be very generous). It still might be legitimate to pay for that, and some research councils pay a compensation for reviews. Are you well suited for reviewing the call? That would indicate that they did some research and they are well informed.
Still, it might be a spearfishing attack, so tread with care.