Instead of writing, “We can’t refund your money until you remit your expenses,” turn that sentence around and make it positive:
“As soon as you remit your expenses, we will refund your money.”
Some of the most appealing and persuasive words in the English language are please, thank you, yes, free, save, new, results, easy, money, now, guarantee, discovery, health, sale, safety, proven and love.
If you use those words, make sure you are using them accurately. When you make promises, keep them.