Not enough info. Did you restore stock recovery? Why can't you install OTA (what error messages, etc.)?

Did you turn it back to S-on after doing S-off? If so, you didn't need to, as s-on is not required for OTA.

What is the current state of the phone, is it bootlooping, etc.?
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Phone: AT&T HTC One (M8)

Tablet: Samsung Galaxy Tab Pro 8.4 (WiFi only)