If you want help, it would be most helpful if you could provide the community with the basics of what you are doing. We can guess you are trying to create a fulfillment, but that leads to many questions. There is the old RestAPI version of doing that. There is the newer GraphQL version of that too. And the fulfillmentOrder mutations.
So without knowing what you are doing, it is hard to help you out. Sure, we know you have a location. Awesome. But what else is going on?
As an example, I had a situation where I could not deal with an inventory update that also needs a location. Why? The error was "Location is no longer valid", even though it was perfectly valid! So the only recourse was to provide Shopify with the respond header ID so they can investigate. So if you are getting an error like that, one you do not believe in... get the response, and provide it here! Then you get help!