Provide consultancy on Bitcoin Core RPC

Hello,

We are developing website where we use Bitcoin Core as wallet and our users create addresses on that wallet and transfer BTC to each other. We have also withdrawal functionality which allows to withdraw bitcoins from their internal address to any external address.
This project is looking for consultants who can help to fix a problem(error) which we get when transferring bitcoins from internal address to external.
PHP knowledge will also help you to understand the code we use, but if you proficient in Bitcoin Core RPC its enough for us generally.
More details

Here is the stack of RPC methods we use to send to address:

1)createrawtransaction
2)fundrawtransaction
3)signrawtransactionwithwallet
4) sendrawtransaction
Details will follow once you contact.

The sending works if you send once in 10 hour, but if you try to send more frequently we get bad-txns-inputs-missingorspent error.

If you are available for this consultation please contact me.

Thank you!