Payment is taken as the final step of the investment process on the Equivesto platform, right after you have signed all of the documents.
The documents you sign are a Subscription Agreement (essentially a purchase agreement for the shares), a Risk Disclosure Form, an Investment Limit Confirmation form, and a Joinder Agreement (adds you to the company's shareholders' agreement).
Once a subscription agreement is signed, payment should immediately follow. A subscription agreement is a legally binding document that should not be taken lightly. It is confirmation that you understand the terms of an agreement and will purchase shares at the agreed upon price and quantity.
Don't fret, on Equivesto there is a 48 hour cool-off window for you to change your mind. You can ask for a full refund within 48 hours of investing with no questions asked.