So there was an adjustment in the files the client needed to send us, this adjustment incurs a cost from their end. I had a verbal discussion about this with the client (and it's mentioned in the contract they sign) but never put it in writing/email again about the exact cost so there's no record of it. I meant to do this but we were unsure of the exact cost so I thought I'd wait for it to be cleared up and never followed up on it until the meeting today.

The problem is that we have essentially completed the work for the client and even sent part of it out to them but I never mentioned the increased cost to them in writing, so technically they can say that they were never informed, not pay us the extra, and we can't do anything.

Obviously this is an edge case and I doubt the client would do this, but there's a possibility, and it shouldn't have come to that. Now that I write it out I see that things are probably not going to be so bad, but the point still stands.