Marketplace Shop

I have a marketplace shop he is okay and everything works my only problem is when I buy in my marketplace shop a worth of 1000 crypto tokens he gets this error message "invalid BigNumber string (argument =" value ", value = "1.2e+21", code = INVALID_ARGUMENT, version = bignumber/5.5.0) "now I'm looking for someone who can fix it. my budget for this is 15$ only,, no more higher if you offer morethan 15$ dont message me thank you, because it's just a simple task, because the developer of my marketplace shop is just on vacation so I'll just let others do it first thank you very much