Do you have to sit straight while meditating, or can you lean back on something?

I normally sit straight while I'm meditating but I already saw some people meditating lying in bed, I don't really know how that works 😅
It's Insential to have a good posture while meditating , so maybe you can lean back on something if your posture is straight ? I'm sorry I don't really know

No matter how you sit, your spine should be as straight as possible.If you tend to slouch forward or sway slightly backward, now is the time to gently remind yourself to come back into the character posture. Continue to root down true your body with each Exhale

Either sitting straight, especially for the morning wake-up session or laying flat on the bed, especially when fighting panic or sleepless nights.