Sometimes a company will offer a reward to its investors. Think of it as a gift from the company to you, thanking you for your support of the company.
A reward might be a free product, a discount, dinner with the founders or naming rights for the company's next product launch. A company may also offer different rewards based on investment tiers.
Take a look at the company's investment page on Birchal to see if they are offering rewards.
You are not required to accept a company's reward. You can simply select the 'No Reward' option when investing.