The method isActive() does not exist on Omnipay\Common\GatewayInterface. It seems like you code against a sub-type of Omnipay\Common\GatewayInterface such as Paytic\Omnipay\Euplatesc\Gateway or ByTIC\Payments\Gateways\Providers\Paylike\Gateway or Paytic\Payments\Librapay\Gateway or Paytic\Payments\Payu\Gateway or Paytic\Payments\Stripe\Gateway or Paytic\Payments\Twispay\Gateway or ByTIC\Payments\Gateways\Providers\Romcard\Gateway or Paytic\Payments\Mobilpay\Gateway or Paytic\Payments\Simplify\Gateway or Paytic\Payments\PlatiOnline\Gateway.
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Ignorable by Annotation
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If this is a false-positive, you can also ignore this issue in your code via the ignore-call annotation