Enterprise and govtech founders: what do you do when your clients don't collaborate in the onboarding/setup phase? [I will not promote]

I'm a govtech founder, we closed with our first local gov recently. The kickoff meeting with the team went super well: we agreed on who is responsible for what and the next steps. They also agreed to send us a number of files to prepare our product for them. Problem is that after the kickoff the team was not really collaborative, they didn't send all the stuff that we need, even after some nudging. I'm now not sure on what to do, shall we just make the best out of what they sent us with the risk of having a product that it's not really working well for them or shall we continue to insist in having everything that we need to give them the best product possible? How do you approach these situations?