chore: update referral logic

src/modules/referrals/entities/referral-reward.entity.ts

@@ -16,8 +16,8 @@ export class ReferralReward extends BaseEntity {
   @ManyToOne(() => Referral, (referral) => referral.rewards)
   referral: Referral;
 
-  @Column({ type: "decimal", precision: 10, scale: 2, nullable: false, transformer: new DecimalTransformer() })
-  amount: Decimal;
+  @Column({ type: "decimal", precision: 10, scale: 2, nullable: true, transformer: new DecimalTransformer() })
+  amount?: Decimal;
 
   @Column({ type: "enum", enum: ReferralRewardStatus, default: ReferralRewardStatus.PENDING })
   status: ReferralRewardStatus;