built an internal tool to save our dev agency, now turning it into a solo saas. bad idea?

my partner and i run a dev agency and we were bleeding cash flow waiting for clients to pay after signing static pdfs. i got so mad i just coded an internal tool that merges the proposal and the stripe checkout into one single web link. they approve, the modal opens, we get paid instantly.

it fixed our cash flow immediately, so now i am spinning it out as my own solo saas. for those who have transitioned from agency work to a product business, what is the biggest trap i should avoid this first month?