If you are (or were) employed and are entitled to disability benefits, those benefits are usually paid by an insurance company. That company has a contract with your employer, not you.
In order for you to qualify for those benefits when you need them, your employer must have fulfilled their part of the contract of insurance.
You may have a claim against your employer when the insurer does not pay. Or you may have to prove to the insurer that you are entitled to benefits under the contract.
Long term disability claims are based upon contract. The contracts are complex. Appropriate medical documentation will be required to support the claim and the corporate or insurance appointed doctor may not use the language required to get the job done.
Often some direction is needed as to what questions are required for legal purposes. We know how to do this. Hutchison Oss-Cech Marlatt has had success promoting long term insurance claims to insurers and also insisting on compensation against them when they refuse to pay.