dear statalist

hello
i try to use panel data with 'ppml_panel_sg' gravity model

i want to add time-varying fixed effect and pair fixed effect

however when i use it, it shows error massesge

Error: the set of origin, destination, industry, and time IDs do not uniquely describe the data
If this is not a mistake, try collapsing the data first using collapse (sum)


Does anyone know why it happens?

Thank you