Shovon Mondal. From your image Chi2≈ 2.56. Rwp and Rexp these values are both high, which usually indicates poor counting statistics, noisy data, or instrumental issues, not necessarily a bad structural model or poor fit.

May increase your no of cycles and also check the background count before curve fitting

A low Chi² with high Rexp and Rwp values during Rietveld refinement in FullProf typically indicates a poor model fit, likely due to incorrect initial parameters, an inadequate phase model, or improper background correction. Check the crystal structure definition, instrumental broadening parameters, and try manually adjusting the background or using a more suitable peak model (e.g., Pseudo-Voigt).