The other thing that you could do is submit a single invoice at this time with a deposit or partial amount due immediately, or within 10 days, or 30. Say 50% or 75% of the total.
With the remaining balance due at the end of the contract. That would be still a single invoice. Allow you to have some working capital while you’re doing the job.
and if you do have a good working relationship with your client, you could easily ask them if this would be acceptable before sending that invoice in.
From what you described, it doesn’t seem like this would be much of a problem for them.