entity savedAndFlushed not found later in the same transaction - spring

Question

I have a loop where I persist in DB some new objects if they are not already existing. (productPrice.product)
But in my loop, it does not find a previously persisted entity (with save and flush), and the re-creation of the entity triggers an DataIntegrityViolationException because my unique constraint is violated (ERROR: duplicate key value violates unique constraint "uk_product_b2c_ext_id")
Here is my code (simplified). I don't understand why it doesn't work.
#Transactional(propagation = Propagation.REQUIRES_NEW)
public void myFunction(List<ProductPriceCatalogResponseAPI.ProductPrice> productPrices) {
for (ProductPriceCatalogResponseAPI.ProductPrice productPrice : productPrices) {
ProductPriceB2C pp = new ProductPriceB2C();
pp.setProduct(productB2CRepository.findByExtId(productPrice.getProduct().getId())
.orElse(createNewProductFromExtId(productPrice.getProduct())));
productPriceB2CRepository.saveAndFlush(pp)
}
}
private ProductB2C createNewProductFromExtId(ProductPriceCatalogResponseAPI.Product product) {
ProductB2C p = new ProductB2C();
p.setName(product.getLabel());
p.setExtId(product.getId());
log.info("Persist product {} with external id {}", product.getLabel(), product.getId());
return productB2CRepository.saveAndFlush(p); // Exception here
}
ps : there is no cascade at all between ProductPrice and Product
Here is the code of my entities :
#Entity
#Table(name = "product_b2c")
public class ProductB2C {
#Id
#SequenceGenerator(name = "product_b2c_generator", sequenceName = "product_b2c_id_seq", allocationSize = 1, initialValue = 10000)
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "product_b2c_generator")
private Long id;
#Column(name = "ext_id")
private Long extId;
#Column(name = "name")
private String name;
// getters and setters
}
#Entity
#Table(name = "product_price_b2c")
public class ProductPriceB2C extends AbstractAuditingEntity {
#Id
#SequenceGenerator(name = "product_price_b2c_generator", sequenceName = "product_price_b2c_id_seq", allocationSize = 1, initialValue = 10000)
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "product_price_b2c_generator")
private Long id;
#ManyToOne(fetch = FetchType.LAZY)
#JoinColumn(name = "product_id")
private ProductB2C product;
// other fields
// getters and setters
}