If you had 30k to invest in your business - what would you spend it on?

Marketing marketing marketing

I will use $25,000 to learn about fb ads (course,testing, or books) , and the remaining, I will use for something else, like hire copywriter and profreading services (my english not that good)

Marketing all the way. 30k is quite a good amount of money so I could define the best strategy where and how to invest it.

Assuming favorable ratio of Lifetime Value : Customer Acquisition, I'd put aside $25K to acquisition. The remaining $5K for operations (including legal, tax filings, cloud costs, etc).

Have a developers' convention then put my banner, ads everywhere and talk to the devs. . .

User research and Marketing. Also, I only need 5k, you can keep the 25k for now.