merkle supports sending transactions in either base58 or base64 via the standard sendTransaction Solana method. Your custom RPC endpoint can be found in the merkle dashboard.
Example of a request:
{"method":"sendTransaction","id":1,"params": [ # raw transaction encoded either in base64 or base58"AaIUryZ/KC2bPJGgcQucHK+5hi9Iw0VQozc16sl+JPpyPrrM3gg5hqLd4ebW06G5N/3zKhSFxFgFVd0VKtEbNAQBAAECNwS6f7cAt7jzjBXxmPK4DP/hxHGbTEZ15SzDDknfVZ8AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAfyjZKitbMyZDjPFFBM+E8MRJ+vy2H57N179hD40M1dAQECAAAMAgAAAAEAAAAAAAAA" ]}
Example of a response:
{"id":1, # signature of the transaction"result":"4Ex6DuVoyxfwpBaeT2UVbHDZthwF6DRFyRt2Hu2yzZ58awrdC1yXp1Eh9koxhUbk1yrSFPRGqjMM53eRMLQXPXV5"}