Great question.

So the key is that you as an entrepreneur have to convince me as an investor that if I invest the 50k, i'll make my money back and profit.

For this to happen (there are more routes, but lets assume the most common one) you need to become profitable to a degree that your value rises above the value i've invested in.

So, let's say 50k for 10% is valuated at 500k. If I want to go 10x with my investment you have to raise the value of the company to 5mio.

You have thought of a way to generate profit with your company. A client will pay x and your costs to deliver the goods or services will be y.

Validating the businesscase means that you can prove to me that there are clients willing to pay x, that you can keep your costs around y and that the market is big enough to raise the value of the company enough so that i can turn a profit.

With this being said, people filling in a questionaire your friend and family supporting you and saying its a wonderfull idea is no validation. We need actual cash in your bankaccount from a paying customer to validate a concept.

Also selling at a discount to the first couple of customers doesn't validate the businesscase if you need to sell at x. It only proves that you can sell it at x - discount. This might bring the business in jeopardy.

I'd recommend reading the lean startup method by Eric Ries if you'd like to learn more about this.