[add]: Update loan status after repayment

app/models/repayment.py

@@ -1,4 +1,5 @@
 from datetime import datetime, timezone
+from app.api.enums.loan_status import LoanStatus
 from app.extensions import db
 from app.models.customer import Customer
 from app.models.loan import Loan
@@ -29,8 +30,11 @@ class Repayment(db.Model):
 
         # Check loan exists
         loan = Loan.get_customer_loan(loan_id = loan_id, customer_id = customer_id)
-        if not loan:
-            raise ValueError("Loan not found for customer")
+        
+        # Check that the loan is active
+        if loan.status != LoanStatus.ACTIVE:
+            raise ValueError(f"Repayment cannot be processed. Loan status: ({loan.status})")
+        
 
         repayment = cls(
             customer_id=customer_id,