Grading is not a problem. What should I do if the background paper for photography is seriously reflective?

I think it's a paper problem. Everything you can see will reflect light, but the degree of reflection is different You can't see anything if you don't reflect light. Try dimming the flash with a soft mask or something. Moreover, the official map given by the landlord is not comparable, and people may use several sets of lights to eliminate the problem of reflection.