CC2340R5: Is SimpleLink data encoded?

Part Number: CC2340R5

Tool/software:

Hi,

How is the payload data encoded when using SimpleLink with this Chip? We like to have a compatible FSK communication with other FSK chip sin the 2.4GHz band. When decoding with SX1280 or GNU Radio SDR it looks like there is an exchange of the nibbles inside each byte and a shift of the byte when the lowest bit is active. To me this looks like some data withening is active but disabled. Is there some special proprierary data handling in SimpleLink?