really_a_banana, it's important to us that all of your intended contacts receive your messages. I welcome the opportunity to assist with this matter. Since you're able to receive texts from your friend but they're not getting yours, the first thing we'd recommend is having them check their Settings>Messages>Blocked just to ensure that your number wasn't somehow inadvertently added to that list. If your number isn't in that specific blocked section (only under Messages) and the issue still persists, please let us know.
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