If you cannot sync the exchange via API, please make sure that:
You are using recently generated API keys. Sometimes the API key will expire, particularly if you are using it with other services.
You have have recent transactions on that exchange. Some exchanges only have a limited amount of historical data available via their API. If this is the case you will need to upload via the exchange CSV import (if available), or select the manual CSV option and import the data manually.
You have granted the correct permissions. We usually detail the permissions in the instructions, but generally speaking you need to create read-only access to the transaction/ledger history. Only ever add read only permissions. Do not add keys that enable trading or transfer of funds.
Make sure you have completed KYC on that exchange. Many exchanges block access to historical data if you have not yet completed KYC.
If you have checked all of the above and it is still not working, please reach out to support with the exchange name so we can investigate further. Sometimes the exchange has updated their API format and you are unlucky enough to discover this before us.