The club is still paying massively for the incompetence of the past transfers and giving out contracts like confetti to mediocrity. So you could be right about the liquidity issue.Or we just don't have the cash they want upfront /not part of clauses so spend on one player. I feel this would be moving a lot faster if we really had the liquidity to give Dortmund the terms they want. It's not in our interest either to drag this one.
The interest rates are at a historical low at this moment in time and I would expect them to remain so over the next decade. It won't be a massive hit even if they did pay upfront. That's obviously assuming the banks will provide the required facility and the club is up for the risk.