Acute pain is a symptom. Chronic pain is a disease. Most chronic pain is not directly connected with a root cause. Spinal MRIs for example are poor predictors of spinal pain. It is an upmodulation of pain sensation in the peripheral nervous system/brain stem. It isn't mental and it isn't psychosomatic - it is very real. And you can't just ignore it - although there are techniques in pain psychology that help. This is…
While some research shows changes in the brainstem, fMRI shows differences in blood flow in various parts of the brain associated with processing emotions. Right now we don't have a definitive answer as to what causes chronic pain. But we do know for certain that the parts of the brain dealing with pain are also involved in emotional processing.
It's actually very easy to demonstrate to yourself that pain can be psychosomatic. If you're riding your bike and imagine falling off, you will experience real pain. (At least, it happens for me, and I assume I'm not the only person who that happens to).
Here is an interesting fMRI study looking at the effects of pain processing in both fibromyalgia patients and healthy participants:
https://onlinelibrary.wiley.com/doi/abs/10.1016/j.ejpain.200...