The person receiving your message cannot hear the friendly tone you imagined while writing it.

Writing carries your tone in your own head and none of it on the page. The warmth, the joke, the slight hesitation that would soften a request are audible to you as you type and completely absent on arrival, where the reader supplies a tone from whatever mood they happen to be in. Short and neutral often lands as cold.

Read a message back as though you disliked the sender before you send it. Add the small explicit warmth you were only imagining. For anything genuinely delicate use your voice, since a two minute call prevents a two day misunderstanding.