A Sweetwater Spa is made by Sundance. You can call Sundance with the serial number of the spa (usually located on the inner control panel or on a tag at bottom of spa) and they can give you the correct year so you can find a manual also.
FL1 error is a flow error code. Look to see if the spa has "valves" on each side of the pump system. They are usually "t" handles that slide up and down. They may have a plastic piece on the t-handle to prevent them from closing, however if they don't and they are part way closed this could be a problem.
If that is not the problem, check the filter. If it is over 2 years old it could be it needs to be replaced. I would recommend replacing this anyway as it has filtered out other people's waste - yes I know...yuck! An older filter (or dirty filter) can inhibit flow causing this problem after a few minutes.
And last of all it could be the flow switch (pressure switch) is bad and "thinks" there is not enough flow. There may be a Sundance dealer in your area. YOu could call them with the address and see if they have the spa on file. If not Sundance may have a registration on it. There is a link embedded on SUndance above. At the top of the page is a dealer locator, and at the bottom is a link to manuals where you may be able to locate yours where a parts break down is located.
Since the tub is running for 4-5 minutes before the error it is unlikely that you have an air lock, but you could have air getting into the system so check the unions at the front of the pump and be sure there is enough water in the tub.
I hope this helps as the flow error is one of the most popular errors we see. Happy Soaking!