How do I avoid a overbooking when 2 customer pays at the same time?

when reserving seats at a venue, you normally have a number of minutes to complete the transaction before your reservation is removed

in this case the website is temporarily removing the seat from availability.

if it's a hotel room or something like that, you need to have a place where the fact that someone is in the process of ordering is maintained, and released again if they go away.

Isnt this exploitable by your competitors by reserving many seats and not completing the transaction and repeating it again?

Isnt this exploitable by your competitors ..

If you have to be that concerned about it, perhaps it's something to not mess with, do something else, another project, etc.

Only involve yourself in an endeavor with very high integrity.

How do I avoid a overbooking when 2 customer pays at the same time?

@Eco012390 The probably of two people submitting a payment and then those payments being handled at the exact same time is very, very low.

If you’re worried about this then as @snapey says, put some form of “reservation” in where a user has a certain number of minutes to complete their purchase. If they don’t complete their purchase, their reservation is released and made available to customers again.