Self Employed Tax deductible Donation Question (Washington State)

I live and work in Washington State. I have a LLC. I have donated (and am about to do more) some of my services to some nonprofit organizations in my area and I wanted to make sure that I am doing/ receiving everything necessary to make sure the donations qualify for when it comes time to file my taxes.

 

Previously I have sent an email laying out what the services will be and what the donation amount is and ask for a confirmation from the non-profit, clarifying that they accept the donation. What I don't know is if I need anything more or different than that for tax donation purposes.