TypeORM ManyToMany Juntion table create not working

I've got two tables services and offers. an Offer can have many services and a service can have many offers.

My service entity

@Entity('Services')
export class ServiceEntity extends BaseEntity {
 
  @PrimaryGeneratedColumn()
  serviceKey: number;
  
  ....
  
  @ManyToMany(() => OffersEntity, (offer) => offer.services)
  @JoinTable({
    name: 'offersXservices',
    inverseJoinColumn: {
        name: 'offerKey',
        referencedColumnName: 'offerKey'
    },
    joinColumn: {
        name: 'serviceKey',
        referencedColumnName: 'serviceKey',
    },
   })
   offers?: OffersEntity[];

}

And My Offers entity is defined like this:

@Entity('Offers')
export class OffersEntity extends BaseEntity {
  @PrimaryGeneratedColumn()
  offerKey: number;
  
  ....
  
  @ManyToMany(() => ServiceEntity, (service) => service.offers)
  @JoinTable({
    name: 'offersXservices',
    inverseJoinColumn: {
        name: 'serviceKey',
        referencedColumnName: 'serviceKey'
    },
    joinColumn: {
        name: 'offerKey',
        referencedColumnName: 'offerKey',
    },
   })
   services?: ServiceEntity[];
}

I'm getting an error when I tried to create an offer record with some services : query failed: INSERT INTO "offersXservices"("offerKey", "serviceKey") VALUES (DEFAULT, DEFAULT), (DEFAULT, DEFAULT) error: error: null value in column "offerKey" violates not-null constraint.

I don't understand why this is happening? in the above generated query the DEFAULT should be replaced with offerKey and serviceKey respectively. can anyone help me on that?

Here is the code which I use to insert into offer record.

const _offerEntity = await OffersEntity.create({
            vendorKey: input.vendorKey,
            name: input.name,
            description: input.description,
            startAt: input.startAt,
            expiry: input.expiry,
            services: await ServiceEntity.find({
                where: {
                    serviceKey: In(input.services)
                }
            })
        });

 await queryRunner.manager.save(_offerEntity);

Any help would be appreciated :)

PS: Database is postgresql