Some women do not want to forego paid fun even during their period.
Or, shortly before meeting a customer, the period will surprise them if they come unplanned.
Here you can use a sponge (e.g. Beppy's; also in Internet trade) that you insert deep into the vagina and up to the cervix. Depending on the thickness of the period, the sponge can remain in the vagina for up to eight hours, should the period change, and it should be washed out with water (no soap!).
It should only be used once and then thrown away, as germs can form if it is used again. Ideally, you usually do not offer vaginal sex because special caution is required during menstruation. During this time, the vagina is very sensitive to pathogens that can be transmitted via blood and sperm. Viruses, fungi and bacteria find an ideal breeding ground during this time.
If you still want to work anyway, you should limit yourself to practices such as oral sex or hand relaxation. Most customers don't think it's great when they notice that the woman has her period. A sponge usually does not offer enough protection to go unnoticed.