Oh, I am so with you on this! I loathe having to chase for money. It's even worse when it's a government department . What irks me is people who earn salaries who have absolutely no concept of what it is to literally earn every bean.
As you gather, I've been there and am still doing it!
Glad you sorted it and that you were so smart to "quarantine" that amount.
Oh... the government here is pretty good (mostly... although there was that one time when they asked for a chunk of money to be paid to them... and then reimbursed it the next week...).
Yes, the idea of really needing invoices to pay on time... and to be able to keep the cash flow moving and stocking up a reserve to smooth out the dips... it's really annoying and something that really is unique to a freelancer...