Connection error: SQLSTATE[HY000] [1049] Unknown database 'billing_system'<br />
<b>Warning</b>:  Attempt to read property "contract_number" on null in <b>C:\xampp\htdocs\billing\backend\api\create_contract.php</b> on line <b>21</b><br />
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<b>Warning</b>:  Attempt to read property "client_id" on null in <b>C:\xampp\htdocs\billing\backend\api\create_contract.php</b> on line <b>22</b><br />
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<b>Warning</b>:  Attempt to read property "facility_id" on null in <b>C:\xampp\htdocs\billing\backend\api\create_contract.php</b> on line <b>23</b><br />
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<b>Warning</b>:  Attempt to read property "start_date" on null in <b>C:\xampp\htdocs\billing\backend\api\create_contract.php</b> on line <b>24</b><br />
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<b>Warning</b>:  Attempt to read property "end_date" on null in <b>C:\xampp\htdocs\billing\backend\api\create_contract.php</b> on line <b>25</b><br />
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<b>Warning</b>:  Attempt to read property "monthly_fee" on null in <b>C:\xampp\htdocs\billing\backend\api\create_contract.php</b> on line <b>26</b><br />
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<b>Fatal error</b>:  Uncaught Error: Call to a member function prepare() on null in C:\xampp\htdocs\billing\backend\models\Contract.php:22
Stack trace:
#0 C:\xampp\htdocs\billing\backend\api\create_contract.php(29): Contract-&gt;create()
#1 {main}
  thrown in <b>C:\xampp\htdocs\billing\backend\models\Contract.php</b> on line <b>22</b><br />