It’s a fair cop
Definition 1 of 1
Pro Tip 1/3British Origin
Know that 'it's a fair cop' is primarily used in British English, not American English. 
When in the UK, saying 'it's a fair cop' will sound natural, but not in the US.
Pro Tip 2/3Informal Use
'It's a fair cop' is informal and often used lightheartedly or humorously. 
When my mum found the hidden sweets, I chuckled and said, 'It's a fair cop.'
Pro Tip 3/3Legal Context
The phrase can be used in minor legal contexts, like acknowledging small wrongdoings. 
Caught parking illegally, I told the warden, 'It's a fair cop.'