The only invoice that always gets paid is the one they paid before you started.
Invoice after, and wait
Freelancers do the work, send the invoice, and wait. Net 30 turns into net 60. The polite reminder, the less polite one, then "we're disputing hour four." Some clients pay late. Some argue about the number. Some vanish with the work and the invoice.
What Yoursellf does
Clients pay for a block up front, through Stripe, straight into your account. The hours sit in their balance and go down as you work. Nobody can stiff you for work they already paid for.
Short jobs protect you in the other direction too. The first block is a trial for both sides. They see the work. You see whether they pay on time, know what they want, and respect the hours. If it is working, keep going. If it is not, the block ends and so does the engagement.