The payment is donation so there should not be any VAT or other tax
Why would there be no vat or taxes? Are you a charity organisation? Also, the tax benefit is something the giver has, not the receiver. Can I reduce my taxable income for making donations to you?!
While they are called donations, they are in fact not. They are tips. You sell something and people overpay. That your sale price is 0 does not change this. You are generating income. If I "donate" to you on our project, I get access to that project, even if you later put a minimum price on it.
You sure your income was not taxed by income tax? There was a tax interview, was there not? If those "donations" were personal gifts, that would not be necessery, now would it.