iPhone 8 can receive but not send sms

Try first to optimize the range of the mobile network, see this Apple article:

If you see No Service or Searching on your iPhone or iPad

If you see No Service or Searching on your iPhone or iPad - Apple Support

See also -> If you can't send or receive messages on your iPhone, iPad, or iPod touch

If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support

Contact your carrier, and ask about your data paln.

Michael ~ Does your iPhone 8 still have its original battery?

And what's the Maximum Capacity % here?...

Settings > Battery > Battery Health

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