help understanding knox warranty void 1 (0x0500) on my s6/ uk sm-g920f

Hey friends I need some help with a s6 that came to me rooted and had different imei # and therefor couldn't get any signal? I work in a repair shop in canada however the phone is model sm-g920f /uk the guy bought it off amazon and asked me to unroot for the above issue. I checked root checker and knox off all looked good so i used odin with all appropriate corresponding firmware to model but failed and i cant get anything to boot now. the message in dl mode reads:
odin mode
product name:...

help understanding knox warranty void 1 (0x0500) on my s6/ uk sm-g920f

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