I'm a sole proprietor and gave out around 1000$ in prizes for my business' event, either through paypal or e-transfer. How can I deduct this as a business expense? There's not really a receipt.
For an expense to be a valid business expense it has to be "A necessary part of doing business". In other words it has to be something that benefits the business. Things like wages, advertising, office rental, buying computers, all obviously qualify if they are needed to do the business or help it do it better.
Whether giving out a prize qualifies is going to depend on circumstances. Something where potential customers give you their contacts and you give one of them a prize would probably qualify - it generates contacts that will increase the sales. On the other hand if you are giving out a prize for some competition that isn't really related to your field then that isn't going to benefit your business, and it won't be deductible.
If you want to sponsor an educational prize it may be easier to make it a charitable donation rather than a business expense. Most educational organizations are set up as charities and can accept donations and give tax receipts.