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Black-masked (Persaonatus) lovebirds and Fischeri lovebirds are different species. This would create hybrid chicks, which 1. are neither one nor the other species 2.impures the species and 3. are not worth as much money.
Better to get another bird if you want to breed.
No serious breeder is going to pair these two birds together unless they are trying to bring a mutation from one species to the other via transmutation.
If you have these two birds as your pets and they have laid an egg, just boil it for a couple of minutes, allow to cool, and put it back. Dummy eggs for the future would be benefitial.