Record the identifiers
Save machine or game name, provider, venue or casino account, time, stake and round ID.
Check the meters
Compare cash/credit balance before and after the event and any hand-pay or attendant message.
Use the official history
For online play, open round history; for a venue machine, notify staff before leaving or inserting more money.
Ask for the recorded result
Request the server or machine log and the specific correction. A screenshot without identifiers is weaker evidence.
Quick answers
Does a frozen screen prove a void round?
No.
Should the next spin be placed immediately?
No.
What evidence is strongest?
Identifiers, meter values and the official round record.