Cross-Chain Communication: Integrating ICP with Ethereum and other EVM blockchains required understanding and adapting the robust evm-rpc canister that can handle the intricacies of different blockchain networks. I overcame this by implementing an EVM RPC canister from another starter kit and building it up by keeping an eye on the official evm rpc canister.

Secure Payment Verification: Ensuring the security and accuracy of payment verifications with external services like PayPal was critical. I tackled this by using HTTPS outcalls canister to make secure API requests and implementing comprehensive verification logic to validate transaction details.

Real-Time Exchange Rates: Providing accurate and up-to-date exchange rates for various cryptocurrencies and fiat currencies was essential for user trust. I integrated the Exchange Rate canister to fetch real-time rates and used efficient caching mechanisms to maintain performance. Nevertheless, the calls that the canister does to the external APIS does not work in local in my case.

Handling Payable Transactions: Managing payable transactions on the Ethereum blockchain required precise handling of smart contract interactions and gas estimations. I tested and optimized our smart contract functions to ensure smooth and error-free transactions.