ClassNotFoundException Attempted to load class "RajaOngkirLib" from the global namespace. Did you forget a "use" statement?

Is anyone can help me to solve my problems? im really new to php

i always get this error message when i try to purchase from my shop.

Im using API Shipping module From KurirQ

everytime i click purchase on my shop

I always get this error

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Here are the Codes

getKotaById($province_id, $city_id); } if ($city_id && $subdistrict_id > 0) { $kecamatan = $rj->getKecamatanById($city_id, $subdistrict_id); } if ($kecamatan && isset($kecamatan['type']) && $kecamatan['type'] && isset($kecamatan['city']) && $kecamatan['city']) { $city = $kecamatan['type'].' '.$kecamatan['city']; if (isset($kecamatan['subdistrict_name']) && $kecamatan['subdistrict_name']) { $city .= ', Kec. '.$kecamatan['subdistrict_name']; } } else { $city = $kota['type'].' '.$kota['city_name']; } $id_state = Db::getInstance()->getValue('SELECT id_state FROM '._DB_PREFIX_.'rajaongkir_propinsi_to_ps_state WHERE province_id = '.(int)$province_id); $state = State::getNameById($id_state); $this->formFields['city']->setValue($city); $this->formFields['id_state']->setValue($id_state); return parent::submit(); } }