Doing part of a repair yourself and hiring out the rest is a common split. With a service contract, it can cause trouble that has nothing to do with the mechanics. The contract was written around a set of parties, usually the seller, an administrator, and a repairer chosen under its terms. The part you buy may not fit those terms.
Why the part question matters
Many contracts describe which parts they cover and who supplies them. Some say the administrator or repairer will furnish parts. Some allow the repairer to use parts of equal quality. Some state that a part obtained outside the program's channel will not be reimbursed. Other contracts say nothing on the point. Silence is not permission, so ask for the position in writing.
What to read in the contract
Find the clause on repairs and parts, then the clause on who may perform repairs, then any clause on owner-supplied materials or on parts the owner obtained. Read them together. A clause that allows any licensed repairer may still refuse a claim if that repairer is not authorized to accept a part you bought yourself.
Questions to ask before you buy the part
Ask the administrator, in writing, whether it pays for a repair in which the owner supplies the part. Ask whether the part must be new, whether it must carry a manufacturer warranty, and whether the repairer must install it under the contract's own authorization. Ask who decides that the part is the correct one for the fault. Ask what evidence the administrator will want, such as the part's identification or the invoice. Keep the answers with the contract.
Compare the paths on the same terms
The usual routes are these. You buy the part and the contract's repairer installs it. The repairer supplies the part and bills the claim. Or you buy the part and install it yourself, which many contracts treat as an owner repair that can end coverage if the contract says so. Each route has its own terms. Lay them side by side and mark three points: the step where you hand over money, the step where the contract says the part must match, and the step where someone signs that the repair was done.
Keep the paper trail
Retain the part receipt, the repairer's written record naming the part and the fault, and any reply from the administrator. If a claim is later questioned, those papers usually settle the matter faster than memory does. This is an explainer of how contracts commonly work. It is not a promise that any claim will be paid.
Where the rules and rosters are
Who may sell a contract, and whether the state publishes a roster of sellers, depends on the state. This site's state pages give the regulating body, the statute or program cited, whether a roster is published, and the as-of date on each roster where one exists. For example, the Florida rules and roster page is at https://statecoverageindex.com/florida.html. This explainer does not read the contract you hold. Compare your own paper against the state page and the questions above. Where a state page says the state has not been read in this edition, treat that state as unread.