I wanted to ask how can the nonce problem be solved?

I'm referring to the value that in each transaction indicates the number of transactions sent by a certain account which, in Ethereum is called "nonce", in my case (I'm writing a custom connector for an unsupported blockchain) it is called "sequence number". When I send multiple transactions from the same account, the nonce value often doesn't match the expected one because there are already transactions queued on the blockchain for the account. In fact, in my case this information is obtained from the blockchain which only takes into account completed transactions. Saving the nonce offline might be a solution but how to ensure that the transaction with nonce 1 is sent before the transactions with nonce 2 in an asynchronous context without serialization? How is this thing solved in already implemented connectors?