code: def check_paypal_api_key(app_configs=None, **kwargs):
  	
  	messages = []
  
  	mode = getattr(djpaypal_settings, "PAYPAL_MODE", None)
  	if mode not in VALID_MODES:
  		msg = "Invalid PAYPAL_MODE specified: {}.".format(repr(mode))
  		hint = "PAYPAL_MODE must be one of {}".format(", ".join(repr(k) for k in VALID_MODES))
  		messages.append(checks.Critical(msg, hint=hint, id="djpaypal.C001"))
  
  	for setting in "PAYPAL_CLIENT_ID", "PAYPAL_CLIENT_SECRET":
  		if not getattr(djpaypal_settings, setting, None):
  			msg = "Invalid value specified for {}".format(setting)
  			hint = "Add PAYPAL_CLIENT_ID and PAYPAL_CLIENT_SECRET to your settings."
  			messages.append(checks.Critical(msg, hint=hint, id="djpaypal.C002"))
  
  	return messages
docs: Check that the Paypal API keys are configured correctly