Reactive Resume is fiscally hosted by Open Collective Europe, which technically gives the project a "non-profit" status.
The motto of Open Collective is transparency. As a public-facing non-profit project, you can visit the project's collective page to view a list of expenses and invoices incurred over a period of time. All funds raised are dedicated to covering these costs.
You, as the sponsor, have full visibility into where your money is being spent, and how it has impacted the development of Reactive Resume first-hand.
You have the option to sponsor a recurring amount, which will contribute to maintaining a steady foundation for future server costs. Alternatively, you can make a one-time donation, which would also greatly support the project and myself.