If you do not get a chit from a FILM production ask the ADs on set and if it is not resolved on set inform us straight away, on films this is the proof you worked and payment can ONLY be made, if production, you and us, have a copy.
On television and commercial productions this is different (a chit isn’t issued) however it is advisable to keep a record of the hours you worked and if excessive overtime is incurred, or if you think you have been featured, rather than simply a background artist contact the project manager the day after the shoot.