Error message when trying to look at or pay the bill - HELP

[jamesbondss]

 

Hello, everyone! I'm new to WHMCS, so I'm hoping I can find a way to fix the error below, which shows up when my client looks at their invoice or tries to pay it.

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Whoops\Exception\Error

Cannot redeclare getadminpermsarray() in:0

Stack history:

#0 /home/username/mywebsite.co.uk/vendor/whmcs/whmcs-foundation/lib/Utility/Error/Run.php

(0): WHMCSUtilityErrorRun->handleError(1,'Cannot redeclare...',",0')

#1: WHMCSUtilityError [internal function]

Run->handleShutdown()

#2 {main}