My husband's application has been refused

Reason: We diddnt provide sufficient evidence of me of exercising treaty rights in the UK.
With the application we sent my payslips. But they diddnt accept the payslips because it cannot be verified ( official templates, watermarks). They say the cannot verify if this have been altered or tampered with.
Thats why it cannot be considered as evidence of treaty rights as the contents of the payslips printouts have not been authenticated by the issuing party as accurate.
My question: Can they refuse the application on this base? I mean where do they say that your payslips should have the above requirements? They only ask for payslips and they dont say your payslips should look like this...
Plzz can someone help me?? I just dont know what to do