More information is needed. What directions from balboa did you follow? Can you link the information?
Testing voltage should never result in sparks, and running 220v feed to a GFCI subpanel and installing a breaker into your main panel and wiring it to the subpanel shouldn’t be attempted unless you have a fairly good level of skills with home wiring. As you saw sparks when you attempted to check voltage tells me you shorted something to cause said sparks. There is a lot of electronics in a modern hot tub and they are sensitive to stray voltages jumping around with things sparking.
You should have 220v coming out of your main panel where you connected the wires to the new circuit breaker you installed. It should be rated for the current draw of the tub something like 50a. the wiring to the tub has to be sized based on the current and the length of the run. Something like 6 or 8 gage copper. Where it runs thru the house code has one set of rules on the type of wire and where it exists the house another. There is also code requirements on where the GFCI sub panel can be located relative to the tub and the size of wire and the type of conduit it has to be run thru getting to the tub. Lastly the tub has to be connected to the power in the proper way at the correct connections.
None of this work is to be done with the power energized. With the exception of carefully checking voltage with a proper meter set to the correct settings.
If when you took the reading your test probe contacted something else a source of ground etc at the same time as the hot connection that’s when you get a spark. If that stray voltage found its way onto a circuit card it could have easily fried it. when the spark happened did the breaker trip or did the GFCI trip. If they did you did reset them?
We can try and help and verify you have things connected to the proper points with a photo of the connections. Make sure all the above is done correctly for the safety of you and your family.
