What does no withdrawal bleeding mean?

To @Natalka19: In some cycles, withdrawal bleeding may not occur at all without a specific cause - as described by the manufacturer of Belara tablets, there are such cases: "After 21 days of taking the product, withdrawal bleeding usually occurs. In isolated cases, and especially in the first months of taking the pills, withdrawal bleeding may not occur, However, this does not necessarily be a symptom of a decrease in the effectiveness of contraceptive protection. If withdrawal bleeding does not occur after one cycle of tablets in which no film-coated tablet has been missed, the tablets have not been interrupted for more than 7 days, no other medicines have been used concomitantly and there is no vomiting or diarrhoea, pregnancy is unlikely to occur and Belara may be continued. However, if these recommendations for the use of Belara were not followed before the first absence of withdrawal bleeding or if bleeding did not occur in two consecutive cycles, pregnancy should be excluded before continuation of hormonal contraception."

Test result negative, what could be the reason?