Freelance friends, do you often have clients who take a long time to pay you?

I'm a little late to the party here, but you should check out the product I'm working on... fixes this problem -- and you'd be supporting a fellow indie hacker, too! :)

--> Ditto

For now I have had 4 "important" clients: 2 paid on time and another 2 late... and I need to sue 1 of them.

Of course, I won't work with these bad clients anymore, but for me it's hard to know this at first.

I'll use your advice, I'm reading good ideas here!

We charge 50% upfront to start and 50% on completion. I'm also transparent with my Clients that we are an early stage startup without an accounts receivables department so need to collect upfront and have 5-day payment deadlines. Also, if the Finance process takes too long, the client can pay the Stripe invoice (usually few thousand dollars) with a credit card and expense it.

Nope. Because any client who takes too long to pay me isn't a client for long :) why bother dealing with this when there are plenty of clients out there who will pay you promptly?

I read an article a while back from Xero that said the best terms to get paid was NET14. That is full settlement within 14 days.

I use an automatic email reminder that triggers an email a few days prior, a day before and then nags them if they are late.

You could opt to stage the work and not put it live until they've paid.

Fairly common. I started adding a 1% late fee to my contracts. It's not much money, but people don't like being charged fees. It hasn't eliminated companies paying late, but it has seemed to reduce the occurrence.