I see posts with people giving their whole life story to their manager and in the end, they don’t care and it gives them too much info and, perhaps, leverage over you.
In Germany you just say “Hi (name), I will be out sick today. I will provide a doctor’s note when I receive it. Thank you”
That’s it. And the fact that a manager texts you on your personal number? That’s fucked. When you work 09:00am – 5:00pm that’s the only time you should be working or answering emails or texts.