This can be stated in active form. Alternate translation: "Because this service has tested and proven you" (See: [[rc://en/ta/man/jit/figs-activepassive]])
The abstract nouns "generosity" and "contribution" can be stated respectively as an adverb and a verb. Alternate translation: "what you have contributed generously" ([[rc://en/ta/man/jit/figs-abstractnouns]])